Methylene blue and acid red adsorption on biochar made from modified sugarcane bagasse: A dynamic,equilibrium,and thermodynamic investigation

Abstract

This study synthesized biochar adsorbents from chemically activated sugarcane bagasse using ZnCl₂ at pyrolysis temperatures of 400, 500, and 600°C. The modified bagasse biochar was used to remove methylene blue (MB) and acid red (AR) dyes. The surface characteristics of the modified bagasse biochars were analyzed using Scanning Electron Microscope (SEM), Fourier Transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) analysis. Batch adsorption experiments were conducted to assess the impact of various parameters on adsorption performance. Among the different bagasse biochar samples, Zn-BC-600 exhibited superior adsorption capacities for MB and AR with values of 182.225 and 43.324 mg/g, respectively. The adsorption efficiency was significantly influenced by pH, with optimal conditions at pH = 6.0 for MB and pH = 2.0 and 10.0 for AR. The adsorption process for MB and AR on Zn-BCs followed a pseudo-second-order kinetic model, indicating chemisorption as the primary mechanism. Adsorption isotherm studies revealed that Zn-BCs conform to the Freundlich model, proposing a multilayer adsorption due to the heterogeneity of the biochar surface. Regeneration experiments indicated that Zn-BCs could be reused for multiple adsorption cycles. In conclusion, the modified bagasse biochar showed strong adsorption affinity for both MB and AR, particularly for MB, making it a promising adsorbent for treating printing and dyeing wastewater.

Keywords

biochar bagasse methylene blue acid red dynamics isotherm

Introduction

As living standards improve, the use of dyes has expanded across various industries, including textiles, paper, and leather, resulting in a steady increase in dye wastewater discharge annually. Dye wastewater not only possesses high COD levels, making it challenging to treat, but it also contains potent mutagenic substances. If not effectively managed, these substances can pose significant risks to human health (Sahu et al., 2020; Pleşa Chicinaş et al., 2018; Yang et al., 2021).

Azo dyes are a prevalent category of dye substances with a vast array of applications. As per available data, the printing and dyeing industry has utilized nearly 3000 varieties of azo dyes in recent decades. Moreover, the global production of dyestuffs has surpassed 700,000 tons (Chung, 2016). Methylene blue (MB) and acid red (AR) are two common azo dyes that possess several azo groups (–N=N–) in their structure. These groups can break down the dyes and generate hazardous substances that may lead to cancer.

Adsorption is a prevalent method for addressing azo dyes, employing waste biomass to generate biochar with high effectiveness and low cost. It embodies the notion of “waste recycling and reduced carbon emissions” and is expected to be widely adopted (Abdel-Fadeel et al., 2022; Wei et al., 2021; Wolski et al., 2022). Chemical activation of biochar significantly increases its specific surface area, enhancing its pollutant removal capabilities. Common activators include ZnCl₂ (Xing et al., 2023), KOH (Cao et al., 2024), ZnO, and K₂CO_3. Biochar loaded with ZnO has demonstrated a 95.19% removal rate for methylene blue (MB) at an initial concentration of 160 mg/g (Yu et al., 2021). Similarly, a composite of ZnO and biochar effectively adsorbed ReO₄⁻, with a maximum adsorption capacity of 25916 mg/kg (Hu et al., 2020). In continuous adsorption experiments using packed bed columns, factors such as bed depth, bed diameter, and feed flow rate significantly affected pollutant removal (Dawood et al., 2019). For instance, Mexicalcite in a continuous-flow packed tower achieved 94.09% removal of Cr(VI) ions at a flow rate of 2 mL/min and a bed height of 6 cm (Cruz-Olivares et al., 2022). However, the adsorption capacity of these materials in treating dye wastewater remains limited, necessitating the search for substances with superior adsorption potential.

Sugarcane bagasse, composed of cellulose, hemicellulose, and lignin, has a highly structured pore surface, abundant hydroxyl and carboxyl groups, and higher carbon content after carbonization. Techniques, such as pyrolysis, hydrothermal carbonization, gasification, and roasting, are used to produce sugarcane bagasse biochar (Iwuozor et al., 2022; Zafeer et al., 2023).These characteristics enable the modification of bagasse through hydrogen bonding and electrostatic adsorption, facilitating the removal of specific pollutants and dyes from water (Omer et al., 2022). With global sugarcane farming yielding over 18 billion tons annually, bagasse is readily accessible and holds significant potential as an adsorbent material.

The purpose of this research was to investigate the potential of bagasse from sugarcane as a raw material for creating biochar to be an adsorbent for the removal of two dyes by employing zinc chloride (ZnCl₂) as an activator at different pyrolysis temperatures. The study evaluated the performance of the bagasse char after modification at varying temperatures and determined the optimal conditions for adsorption through single-factor experiments. Additionally, the research investigated the adsorption process by analyzing its kinetics, thermodynamics, and isotherms of the adsorption process, providing an enhanced comprehension of the mechanization of dye adsorption by biochars. Overall, this research presents a reliable biochar adsorbent for dye removal, which contributes to an in-depth grasp of the dye adsorption process, which could benefit future applications in the dye industry's wastewater treatment.

Materials and methods

Materials and reagents

Sugarcane bagasse come from Yiwu, Zhejiang. Zinc chloride (ZnCl₂), a solution of hydrochloric acid (HCl, 36%), and hydroxide of sodium (NaOH) of analytical purity come from Shanghai Lingfeng Chemical Reagent Co., LTD, methylene blue (MB) and acid red (AR) of analytical purity also come from Shanghai Lingfeng Chemical Reagent Co, LTD.

Raw material pretreatment and preparation of biochar

Pre-treatment of raw materials

The acquired bagasse was subjected to ultrapure water washing to eliminate impurities, followed by drying. Next, the dried bagasse was mixed with 1 L of 1 mol/L ZnCl₂ solution, and the mixture was sealed at room temperature for 12 h. The treated bagasse was then dried for 10 h at 100°C in an oven before being used.

Preparation of biochar

Place 30 g of the ingredient in a quartz boat and insert it into a tube furnace for pyrolysis. Inject nitrogen gas (N₂) into the boat at a flow rate of 100 mL/min. Increase the temperature at a rate of 10°C/min until it reaches 400, 500, and 600°C, respectively, and maintain each temperature for 2 h. Wash the biochar repeatedly with deionized water to remove impurities. Rinse the modified bagasse biochar with deionized water until neutral, then dry and grind it. Seal and label the samples as (Zn-BCs). The carbonization yields for Zn-BC-400, Zn-BC-500, and Zn-BC-600 were 57.67%, 43.88%, and 32.36%, respectively.

Preparation of dye solutions

Table 1 presents the fundamental details of methylene blue (MB) and acid red (AR), while the two dyes were each 1000 mg/L in concentration

Table 1.

The essential information of MB and AR.

Biochar characterization

The absorbance of MB and AR solutions was assessed using ultraviolet spectrophotometry (HACH DR6000), and dye concentration was determined accordingly. The surface area was determined using Brunauer-Emmett-Teller (BET) model with nitrogen adsorption/desorption isotherms at −196°C using the Accelerated Surface area and Porosimetry System (ASAP 2020 HD88). Pore size distribution was analyzed using the Barrett-Joyner-Halenda (BJH) method (Garg et al., 2019). Scanning Electron Microscopy (SEM: Phenom ProX) was employed with a10 kV electron beam for surface analysis. Fourier Transform infrared spectroscopy (FTIR: Nicolet Is50) assessed changes in surface functional groups, with a wavenumber range of 400–4500 cm⁻¹ and a scanning rate of 6.28 cm/s. X-ray diffraction (XRD: D8) was used to investigate the crystal structure of Zn-BCs with θ set at 5–90°. Operating parameters included a tube voltage of 40 kV, a tube current of 40 mA, and an incident wavelength of 0.15418 nm. Finally, the chemical composition of Zn-BCs was analyzed using X-ray photoelectron spectroscopy (XPS: ThermoFisher Nexsa), with an operating voltage of 220 V, an X-ray source wavelength spanning 10–400 µm, and ion energy ranging from 200 eV to 4 keV.

Adsorption experiments

An amount of 0.02 g of Zn-BCs was introduced into 20 mL of both MB and AR solutions the concentration of MB and AR were 30 mg/L and the pH was regulated to neutral. At a temperature of 25°C and a speed of 220 r/min, the biochar and dye combination was swirled for six hours without exposure to light before being filtered. The absorbance of MB and AR could be measured by at wavelengths of 669 nm and 503 nm, respectively. Following this, the concentration of the dye can be calculated by conversion from the standard curves. The removal rates E and adsorption capacities $q_{e}$ of different biochars for MB and AR were calculated according to equations (1) and (2), and parallel and blank controls were set up. The impact of each factor on MB and AR was examined by varying the single factors, such as adsorption time and pH.

E = (C_{0} - C_{e}) / C_{0} \times 100 %

(1)

q_{e} = (C_{0} - C_{e}) \times V / m

(2)

C₀(mg/L) represents the original concentration of the liquor, E(%) represents the dye removal rate, C_e(mg/L) represents the dye concentration after complete adsorption, m (g) represents the amount of adsorbent dosed, q_e (mg/g) represents the total quantity of adsorbed dye after adsorption is completed, V (mL) represents the volume of dye liquor.

Regeneration performance study

To assess the regeneration performance of Zn-BCs, 0.3 g of Zn-BCs were added to 150 mL solutions of MB and AR, with initial concentrations of 250 mg/L for MB and 150 mg/L for AR. Adsorption experiments were conducted as described in experimental step 2.5. After adsorption, Zn-BCs were sequentially soaked in 100 mL of 0.1 mol/L HCl and NaOH solutions, for 2 h each, followed by rinsing with ultrapure water to ensure complete desorption of MB and AR. The regenerated Zn-BCs were then reused for adsorption experiments, repeating this process five times to evaluate their recyclability.

Results and discussion

Characterization of biochars

SEM images of Zn-BC-400, Zn-BC-500, and Zn-BC-600 in Figure 1(a)–(f) demonstrate that after high-temperature pyrolysis with N₂, relatively regular pores were formed inside the biochars. With increased temperature, some macromolecular substances, such as cellulose and lignin, were pyrolyzed into small molecules at high temperatures, forming pores and a fibrous pore structure inside Zn-BCs. This improved the overall adsorption performance of the adsorbent (Wang et al., 2021; Tang et al., 2023). Pyrolysis at higher temperatures led to the formation of more pore structures, particularly for biochar produced at 600°C. Furthermore, XPS and XRD test results reveal that Zn–O particles might appear on the exterior of the biochar.

Figure 1.

SEM images of zn-BC-400 (a × 3 k, d × 5 k); Zn-BC-500 (b × 3 k, e × 5 k); Zn-BC-600(c × 3 k, f × 5 k).

Figure 2 displays the FTIR spectra of Zn-BCs before and after MB and AR adsorption. The spectra showed that the most prevalent functional groups present in biochar before and after the adsorption of MB and AR include –OH (Yang et al., 2021), aromatic –CH (Liu et al., 2022), C=O (Salama, 2018), C=C (Yang et al., 2022), –COOH, CO₃^2– (Sun et al., 2022), C–O (Leng et al., 2015), Si–O–Si. Additionally, due to ZnCl₂ activation, the presence of ZnO was observed in the biochars at wavelengths ranging from 460 to 490 cm⁻¹ (Fahoul et al., 2021; Nadeem et al., 2021; Thue et al., 2022). The functional groups played a pivotal role in facilitating the adsorption process. The FTIR peaks of Zn-BCs exhibited no significant changes before and after adsorption, suggesting the stability of Zn-BCs. However, after the adsorption of MB and AR, a reduction in the absorption intensity of the functional groups was observed, particularly those related to hydrocarbons. This indicated a favorable interaction between the surface functional groups of Zn-BCs and the dyes. These results suggested that Hydrogen bonds and π–π interaction occur when MB and AR are absorbed by Zn-BCs (Wang et al., 2021). Specifically, atoms (such as O and H) within Zn-BCs form hydrogen bonds with MB and AR, demonstrating a propensity for hydrogen bond formation (Kumar and Gupta, 2023).The FTIR research also confirmed that as the temperature increased, the types and amounts of functional groups decreased, with the most significant change observed at 600°C, where C = C/C = O near 1698 cm^–1 disappeared.

Figure 2.

The FTIR spectra of different biochars on MB and AR before and after adsorption: (a, b) Zn-BCs + MB; (c, d) Zn-BCs + AR.

Figure 3 illustrates the XRD analysis before and after MB and AR adsorption. Figure 3(a) and (b) indicate that before and after the adsorption of MB on Zn-BCs, there were obvious diffraction peaks near 25 $\circ$ ,which are speculated to be SiO₂ that were a crystalline phase that stayed in the biochar material after the leaching procedure (Thue et al., 2022).Both before and after the adsorption of MB by Zn-BCs contained significant Zn-O diffraction peaks, with the Zn–O diffraction peak intensity at 600°C being stronger than at 400 and 500°C. Similarly, in Figure 3(b), the corresponding positions of the diffraction peaks of MB are roughly the same to AR, respectively at 31.8 $\circ$ , 34.6 $\circ$ , 36.5 $\circ$ , 47.6 $\circ$ , 56.6 $\circ$ , 62.8 $\circ$ , 68.1 $\circ$ and 69.2 $\circ$ (Chen et al., 2022). Upon the adsorption of MB, there was a significant weakening of the nearby diffraction peak at 25 $\circ$ , this suggests that zinc oxide aggregates were generated from biochar's surface, leading to the destruction of the interlayer structure of the material and the formation of new structures (Wang et al., 2021; Dong et al., 2021; Zhuge et al. ). The intensity of the Zn–O diffraction peak increased significantly, indicating the formation of a complex between Zn-BCs and MB (Sun et al., 2022; Dong et al., 2021; Zhuge et al. ; Nuanhchamnong et al., 2022; Zhang et al., 2022; Dai et al., 2020). Likewise, as shown in Figure 3(b), the strength of SiO₂ falls as a consequence of AR adsorption, suggesting the possibility of complexation between Zn-BCs and AR. The XRD results suggest that Zn-BC-600 is the most appropriate biochar for the adsorption of MB and AR, as Zn–O is exposed on the biochar’s surface, ensuring adsorption performance (Yang et al., 2022; Wang et al., 2021; Chen et al., 2022).

Figure 3.

XRD pattern of different biochar before and after the reaction: (a) Zn-BCs + MB; (b) Zn-BCs + AR.

Figure 4(a)–(h) displays the XPS spectra of Zn-BCs before and after the adsorption of MB and AR. The XPS full spectra of Figure 4(a) and (b) reveals the presence of peaks corresponding to C1 s, O1 s, and Zn_2p in the biochar before and after adsorption. XPS analysis examined the changes in the surface composition and functional group states of ZnCl₂-modified biochars at different temperatures after adsorbing MB and AR. The analysis showed that the primary elements of biochar after modification are C, O, and Zn. The C1 s spectra in Figure 4(c) and (d) show three peaks (287.8, 284.8, and 285.6 eV,) that represent O–C = O, C–O and C = O/C–C groups (Wu et al., 2022), respectively. After completing adsorption., a new peak (291.2 eV) appeared in the C1 s spectra, which means the presence of benzene rings in the molecules of the two colors and symbolizes π–π bonds (Pap et al., 2023). The O1 s spectra in Figure 4(e) and (f) shows peaks at 533.6, 535.5, 532.2, and 533.6 eV, corresponding to O–C–O, C–O/C–OH (Dong et al., 2021) and C–O groups, respectively. After adsorption, the dye molecules occupied the adsorption sites or functional groups on the modified biochar, contributing to the formation of C–O/C–OH O1 s bond. It was observed from Figure 4(c)–(f) that the C–O/C–OH O1 s bonds increased from 25.35% to 35.96%, 31.32% to 45.16%, and 53.15% to 62.88% after adsorption of MB with different temperature biochars at 400, 500, and 600°C, respectively. The possible reason for this is that the OH group increases after MB adsorption with biochars. The modified bagasse biochars also showed the presence of ZnO in Figure 4(g) and (h), the ZnO bonds showed an increase, while the Zn simple substance showed a decrease after the adsorption of dye.

Figure 4.

XPS spectra of various biochars before and after the reaction: MB (a, c, e, g) and AR (b, d, f, h).

Effect of pH

The perfect pH value for MB adsorption, as shown in Figure 5(a) is 6.0, with Zn-BC-500 being the most efficient adsorbent. Between pH 2.0 and 6.0, the adsorption performance of Zn-BCs on MB exhibits an increasing trend, stabilizing thereafter. The adsorption capacities and removal rates of Zn-BC-400, Zn-BC-500, and Zn-BC-600 for MB are 107.774, 109.867, and 108.811 mg/g, respectively, with removal rates of 99.545%, 99.835%, and 99.781%. This phenomenon may be triggered by the protonation of biochar surface functional groups, electrostatic repulsion between the adsorbent, surface-bound H⁺ and the conflicting competition of H⁺ and MB for spots to adsorb. As pH increases, the functional groups of the sample and adsorption solution become deprotonated, forming a negatively charged active site on the surface. Consequently, more MB molecules bind through electrostatic interactions. When the solution's pH approaches neutral, charged MB molecules exhibit the least electrostatic repulsion toward each material, while the π–π dispersion force is at its strongest. As depicted in Figure 5(b), the optimal pH values for adsorption are 2.0 and 10.0. Under these conditions, Zn-BC-600 demonstrates relatively effective adsorption of AR. At pH 2.0, Zn-BC-400, Zn-BC-500, and Zn-BC-600 had adsorption capacities of 28.580 mg/g, 28.522 mg/g and 28.680 mg/g^, respectively, with removal rates of 99.968%, 99.968%, and 99.985%. At pH 10.0, Zn-BC-400, Zn-BC-500, and Zn-BC-600 had adsorption capacities of 27.227, 28.522, and 28.680 mg/g, respectively, and the removal rates were 99.598%, 99.744%, and 99.834%. The high removal rate at pH 2.0 may result from the abundant H⁺ in the solution binding to oxygen atoms or the amino protonation of Zn-BC surface functional groups, creating positively charged binding sites that interact with the negatively charged AR through increased electrostatic attraction; thus, enhancing adsorption capacity. However, the rate of removal decreases as the pH goes from acidic to basic, which may be due to a decrease in H⁺ concentration, leading to a reduction in the number of –OH⁻ binding sites and complete deprotonation of functional groups, consequently causing a decrease in adsorption capacity. Therefore, the optimal pH is 2.0. At pH 10.0, both the adsorption capacity and removal rate increase concurrently, possibly because the adsorption process of AR molecules involves not only electrostatic attraction but also membrane diffusion mechanisms (Tong et al., 2019).

Figure 5.

The influence of pH on adsorption.

Adsorption kinetics

To explore the adsorption processes of MB and AR on Zn-BCs, a number of kinetic models have been employed: pseudo-first order (3), pseudo-second order (4), intraparticle diffusion model (5), and Elovich model (6). Figure 6 and Table 2 point out the fitting outcomes.

Figure 6.

Kinetics and isotherm models describing MB and AR adsorption: (a, c) pseudo-first-order model (PFO); pseudo-second-order model (PSO); and Elovich model;(b; d) intraparticle diffusion model (IPD).

Table 2.

The kinetic parameters of MB and AR dyes onto Zn-BCs.

Kinetics equation	Parameters	Zn-BC-400		Zn-BC-500		Zn-BC-600
Kinetics equation	Parameters	MB	AR	MB	AR	MB	AR
Pseudo-first-order	$q_{e}$ (mg/g)	104.375	29.3121	105.585	26.9724	104.933	29.3056
	$k_{1}$ (1/min)	0.0732	0.0551	0.0659	0.0779	0.2228	0.0755
	R ²	0.9341	0.7725	0.9595	0.9847	0.8486	0.9526
Pseudo-second-order	$q_{e}$ (mg/g)	107.764	29.8964	107.366	27.4863	106.349	29.8526
	$k_{2}$ (g/mg min)	0.0013	0.0035	0.0032	0.0043	0.0075	0.0039
	R ²	0.9796	0.9271	0.9807	0.9861	0.9779	0.9926
Intra-particle-diffusion model	Kd₁ (mg/g min^0.5)	6.5300	2.2307	5.6874	1.0316	3.6936	1.2698
	c (mg/g)	36.0904	10.2342	51.3428	11.5185	82.7388	10.0859
	R ²	0.9862	0.9899	0.8133	0.9442	0.9955	0.9919
	Kd₂ (mg/g min^0.5)	1.1403	0.6534	0.0878	0.9200	0.8378	1.178
	c (mg/g)	87.9914	18.7500	104.240	12.6701	98.4391	8.4895
	R ²	0.9958	0.9832	0.6745	0.9920	0.8535	0.9815
	Kd₃ (mg/g min^0.5)	0.0015	0.0020	5.624E-4	0.0097	0.0047	-0.0248
	c (mg/g)	105.659	29.268	105.621	26.765	105.596	27.5272
	R ²	0.0089	0.1305	0.0342	0.3226	0.8289	0.5747
Elovich	$α$ (mg/g min)	154.009	384.6094	3406.023	276.7594	9.815E17 + 8.9	88.0274
	$β$ (g/mg)	0.0812	0.3882	0.1157	0.4023	0.4385	0.3251
	R ²	0.9441	0.6978	0.9549	0.7597	0.8392	0.9448

pseudo-first-order kinetic model

l n (q_{e -} q_{t}) = (l n q_{e}) - k_{1} t

(3)

pseudo-second-order kinetic model

\frac{t}{q_{t}} = 1 / k_{2} q_{e}^{2} + t / q_{e}

(4)

intraparticle diffusion model

q_{t} = k_{d} t^{1 / 2} + c

(5)

Elovich model

q_{t} = \frac{1}{β} (\ln α β + \ln t)

(6)

PFO and PSO have rate constants of

k_{1}

(1/min) and

k_{2}

(g/mg min), respectively, the total amount of MB and AR adsorbed at time t (min) and an equilibrium state and are denoted by

q_{t}

(mg/g) and

q_{e}

(mg/g),

t

(min) is the reaction time in min, the constants of the Elovich model are

α

(mg/g min) and

β

(g/mg), the intraparticle diffusion model can be illustrated by the constant

k_{d}

(mg/g min 0.5), the extent of the boundary layer can be illustrated by c (mg/g).

As shown in Figure 6 and Table 2, the pseudo-second-order kinetic model aligns more closely with the adsorption of the MB and AR adsorption by Zn-BCs, indicating that chemical adsorption is a significant factor controlling the adsorption process. The time required for MB to reach 95% saturation (t0.95) of Zn-BCs was 128.31 min at 400°C, 108.32 min at 500°C, and 20.16 min at 600°C, respectively. Similarly, the time required for AR to reach 95% saturation (t = 0.95) of Zn-BCs was 128.42 min at 400°C, 112.41 min at 500°C, and 410.24 min at 600°C. In terms of the intraparticle diffusion model, Figure 6(b) and (d) illustrate that the adsorption process involves four stages: solution diffusion, liquid film diffusion, intraparticle diffusion, and adsorption equilibrium. The time taken for solution diffusion and adsorption equilibrium is shorter than that for the other two stages. The fitted curves for both MB and AR are not in line with the origin, which indicated both the particle diffusion step within the adsorbent and the liquid film diffusion mechanism affect the adsorption rate (Wang et al., 2014). In Table 2, as time progresses, the parameter C increases gradually, implying that the external resistance at the final stage of adsorption is considerably high (Heidarinejad et al., 2018). At the initial stage, the elimination of MB and AR is the greatest, owing to the abundance of free binding sites accessible for adsorption and binding with active sites. However, with the passage of time, there are fewer active sites on the exterior of the adsorbent, leading to a slower adsorption rate and a transition from liquid film diffusion to internal diffusion. As illustrated in Figure 6(a), the Elovich kinetic model considers the existence of energetically non-uniform adsorption effects on the adsorbent surface. Comparing the R² values of different Zn-BCs, it was found that Zn-BC-400 and Zn-BC-500 exhibit a higher R² value than Zn-BC-600 during MB adsorption, indicating a better non-uniform surface adsorption effect between Zn-BCs and MB at lower temperatures. On the other hand, as shown in Figure 6(c), Zn-BC-400 and Zn-BC-500 have a lower R² value than Zn-BC-600 during AR adsorption, indicating a better non-uniform surface adsorption effect between Zn-BCs and AR at higher temperatures (Shenvi et al., 2015). Based on the presented kinetic model, the chemisorption procedure takes place both on the exterior and inside the particles.

Adsorption isotherm

The data obtained for Zn-BCs-MB and Zn-BCs-AR were fitted with three conventional isotherm equations, namely Langmuir (7-1) and (7-2), Freundlich (8), and Temkin (9). By comparing the R² values, the appropriate adsorption model was determined. The three isotherm equations are presented below (Yang et al., 2021):

\frac{C e}{q_{e}} \frac{1}{q_{0} K_{L}} + \frac{C_{e}}{q_{0}}

R_{L} = \frac{1}{1 + C_{m} K_{L}}

I n q_{e} = (\ln K_{F}) + (\ln c_{e}) / n

(8)

q_{e} = \frac{R T}{b_{T}} \ln a T c e

(9)

C e

denotes the concentration after adsorption equilibrium in mg/L,

q_{0}

denotes the largest of adsorption capacity in mg/g,

C_{m}

denotes the maximum initial concentration of sorbent,

R_{L}

is a dimensionless separation factor. n denotes the degree constant,

K_{L}

denotes the Langmuir adsorption constant in L/mg and

K_{F}

denotes the Freundlich constant in mg/g respectively, n is the degree constant (Usman and Khan, 2022), T denotes the Kelvin temperature in K,

a_{T}

and

b_{T}

are the model parameters, respectively, R is the thermodynamic constant 8.314 J/(mol k).

Based on the findings presented in Figure 7(a) and Table 3, the adsorption of MB by Zn-BCs exhibited better conformity with the Freundlich models in terms of R² value. Furthermore, 1/n were 0.0537 and 0.9826, which lie between 0 and 1, indicating chemisorption of MB by Zn-BC-400 in the presence of electrostatic interactions. In contrast, the three models more accurately predicted the MB adsorption by Zn-BC-500 and Zn-BC-600, indicating a complex adsorption process that may be regulated by multiple mechanisms. According to Table 3, the Langmuir model calculated $R_{L}$ values ranged from 0 to 1, indicating an efficient adsorption process for MB on Zn-BC-500 and Zn-BC-600 (Cazetta et al., 2011). The largest adsorption capacities are 172.551 and 182.225 mg/g. The 1/n values derived by the Freundlich model (0.1251 and 0.1444) varied from 0 to 1, indicating that chemisorption occurred for the MB (Zeng et al., 2019). The R² values derived by Temkin model was 0.9167 respectively. It demonstrated that the strong intermolecular forces may be existed on adsorption procedure (Liu et al., 2023).

Figure 7.

Isotherms for MB and AR were adsorbed by Zn-BCs: Langmuir isotherm, Freundlich isotherm, and Temkin isotherm.

Table 3.

Adsorption isotherm parameters of MB and AR.

Isotherm model	Parameters	Zn-BC-400		Zn-BC-500		Zn-BC-600
Isotherm model	Parameters	MB	AR	MB	AR	MB	AR
Langmuir	$q_{m}$ (mg/g)	155.789	31.809	172.552	36.163	182.225	43.324
	$K_{L}$ (L/mg)	2.1526	18.2282	1.8319	4.8515	4.7188	0.1653
	$R_{L}$	0.0065	0.0011	0.0084	0.0045	0.0036	0.1202
	R ²	0.8347	0.8040	0.9963	0.9415	0.9167	0.9076
Freundlich	$K_{F}$ (mg/g)	131.5488	27.1294	106.1126	23.1457	130.0676	10.7995
	1/n	0.0537	0.1315	0.1251	0.1233	0.1444	0.3395
	R ²	0.9753	0.9862	0.9774	0.9800	0.9787	0.9777
Temkin	$a_{T}$ (L/g)	2986.0	3355.38	522.01	1491.90	361.01	1.66
	$b_{T}$ (KJ/mol)	0.2859	0.7164	0.1453	0.7493	0.1130	0.2725
	R ²	0.7963	0.9565	0.9614	0.9669	0.9682	0.9077

From Figure 7(b) and Table 3, it can be inferred that the adsorption of AR by Zn-BC-400 conforms better to the Freundlich models. The 1/n values derived by the Freundlich model were found to be 0.1351, which is between 0 and 1, indicating the chemisorptive effective on of AR by Zn-BC-400 in the presence of electrostatic interactions. On the other hand, three models can be fitted well (R²≥ .9077) for the adsorption of AR by Zn-BC-500 and Zn-BC-600, indicating multiple mechanisms at play. As shown in Table 3, Zn-BC-500 and Zn-BC-600 fitted the Langmuir model, and the calculated values $R_{L}$ obtained from the calculations ranged between 0 and 1, which also indicates that the process of adsorption of AR is effective and that the greatest adsorption capacities are up to 36.163 and 43.324 mg/g. The calculated 1/n values using the Freundlich model were found to be between 0 and 1 for both Zn-BC-500 and Zn-BC-600, which were 0.1233 and 0.3395, respectively. These values indicate the occurrence of chemisorption of AR. Furthermore, The R² values derived by Temkin model were .9077 respectively. It demonstrated that the strong intermolecular forces may be existed on adsorption procedure.

Thermodynamic investigation

The $C_{e}$ and $q_{e}$ of Zn-BCs adsorbed MB and AR at different concentrations and temperatures were measured, the following equations can be used to calculate thermodynamic parameters, including enthalpy $Δ H \circ$ , Gibbs free energy $Δ G \circ$ and entropy $Δ S \circ$

Hoff equation : Δ G \circ = - R T \ln (q_{e} / C_{e})

(10)

Gibbs - Helmholtz equation : Δ G \circ = Δ H \circ - T Δ S \circ

(11)

As shown in Table 4, when Zn-BCs adsorb MB and AR,

Δ G \circ

is negative, and the temperature is higher, the value is smaller, indicating that the dye adsorption procedure by Zn-BC happened spontaneously. When the temperature is higher, the adsorption process is more favorable.

Δ H \circ

is positive, indicating that the dye adsorption by Zn-BC happened endothermic

Δ S \circ

is positive, indicating that the adsorbent surface randomness and disorder increase after adsorption (Sahu et al., 2020; Tsamo et al., 2019).

Table 4.

Mb and AR dye thermodynamic parameters.

Biochars	Dye	△G⁰(KJ/mol) 288K	△G⁰(KJ/mol) 298K	△G⁰(KJ/mol) 308K	△H⁰ (KJ/mol)	△S⁰ (KJ/mol)	R ²
Zn-BC-400	MB	−11.550	−12.058	−13.325	14.137	0.0888	.9426
Zn-BC-400	AR	−7.322	−12.075	−13.812	85.631	0.3245	.9328
Zn-BC-500	MB	−11.694	−12.322	−13.648	16.56	0.0977	.9592
Zn-BC-500	AR	−6.596	−12.390	−14.130	101.21	0.3767	.912
Zn-BC-600	MB	−11.842	−12.653	−13.876	17.429	0.0514	.9868
Zn-BC-600	AR	−3.302	−8.875	−13.119	137.85	0.4909	.9939

Reusability study

Cyclic adsorption experiments are a common approach for assessing the robustness and reclamation potential of biochar (Shao et al., 2024). As shown in Figure 8(a) and (c), after five cycles of HCl regeneration, the removal rates for Zn-BC-400, Zn-BC-500 and Zn-BC-600 for MB were 63.60%, 77.13%, and 73.59%, respectively. Similarly, the removal rates for AR were 67.30%, 75.90%, and 81.56%, respectively. According to Figure 8 (b) and (d), when regenerated with NaOH, the removal efficiency of MB improved to 70.30%, 80.28% and 75.22% for Zn-BC-400, Zn-BC-500, and Zn-BC-600, respectively. The removal efficiency for AR was 60.93%, 70.24%, and 73.52%, respectively, after five cycles. Compared to HCl, the adsorption efficiency of MB improved after NaOH treatment, whereas the opposite trend was observed for AR. As the number of cycles increased, the removal efficiency of biochar for both MB and AR gradually decreased. This decline may be attributed to slight losses in the adsorbent material during the regeneration process and incomplete desorption of MB and AR from the internal spaces, resulting in a reduction in binding sites and consequently weakening the biochar’s ability to remove pollutants (Zheng et al., 2024; Liu et al., 2024).

Figure 8.

Recycle of Zn-BCs: (a) MB-HCl; (b) MB-NaOH; (c) AR-HCl; (d) AR-HCl.

Treatment of synthetic dye effluents

The results shown in Figure 9(c) and (d) demonstrate a significant removal effect of Zn-BCs on MB and AR, indicating that biochar is also effective in treating complex dye wastewater. To validate this conclusion, experiments were conducted using synthetic dyes containing common industrial dyes to test the efficacy of Zn-BCs in treating such wastewater. Figure 9(a) and (b) illustrate the UV-visible spectra and photographs of the experimental wastewater before and after adsorption. By calculating the spectral area between 190 and 800 nm, we determined the removal efficiency of dyes and compounds (Cavalcante et al., 2022; dos Reis et al., 2023). The results indicate that Zn-BCs achieved removal rates of 65.1%, 72.5%, and 88.1% for the experimental wastewater, respectively. These findings are consistent with the adsorption experiments, suggesting that biochar modified with ZnCl₂ exhibits superior adsorption performance. Considering the similarity between laboratory-prepared wastewater and actual industrial wastewater, we can conclude that the biochar prepared in this study holds significant potential for practical wastewater treatment applications.

Figure 9.

Treatment of lab-made dyes effluent. (a) Effluent; (b, c, d) synthetic dyes, MB and AR before and after adsorption photos.

Adsorption mechanism

Figure 10 shows the adsorption mechanism and removal of MB and AR dye molecules by Zn-BCs. Based on the analysis of adsorption kinetics, thermodynamics, XPS, and XRD, it can be concluded that ZnCl₂-modified sugar bagasse biochar at different temperatures can enhance both physical and chemical adsorption of MB and AR. The adsorption isotherm models indicated that the adsorption of bagasse BCs was mainly due to chemisorption, and the force of adsorption between adsorbent molecules and adsorbates that was of great significance for adsorption. It appears that the adsorption capacity improved with the pH of the solution, which confirms that electrostatic interaction was critical to the stage of adsorption. The interaction between the makeup of the pores and the H bonds induced the adsorption of Zn-BCs, according to the internal diffusion hypothesis. The XPS analysis discovered the production of π–π bonds between the two dyes and biochars, which led to the interaction between them. Moreover, the adsorption of MB tended to increase the functional group of –OH–, indicating the importance of H bonds in adsorption. The FTIR investigation detected variations in the surface of biochar after the completion of adsorption, and the absence of the –COOH vibration peak at 1698 cm^–1 supported the formation of H bond between biochar and dyes (Wang et al., 2018; Wang et al., 2017). This study discusses the various factors involved in the adsorption process of two dyes, including the porous structure of Zn-BCs, the H bond, electrostatic attraction, intervoid interaction, and the adsorption π–π bond.

Figure 10.

Adsorption mechanisms for the MB and AR on Zn-BCs.

Comparison with other reported adsorbents

The surface areas of Zn-BC400, Zn-BC500, and Zn-BC600 are 717, 771, and 767 m²/g respectively, indicating a slight variation in surface area among the different samples. As shown in Table 5, Zn-BCs demonstrated higher dye removal efficiency for both MB and AR compared to other materials, highlighting the effectiveness of Zn-BCs biochar as a highly efficient adsorbent.

Table 5.

Maximum adsorption capabilities of MB and AR and their BET data.

Adsorbents	Dye water	Adsorbent dosage (g)	Maximum adsorption capacity (mg/g)	BET surface area(m²/g)	Reference
Bagasse	MB AR	0.02	182.3 43.3	771	This study
Chemically modified Lychee seed Biochar	MB	0.02	124.5	154	Sahu et al. (2020)
Sugarcane bagasse	MB	0.1	112.9	1.0180E + 00	Omer et al. (2022)
Sewage sludge and lignin on biochar	MB	0.05	3.06∼38.56	/	Dai et al. (2022)
Fe-modified lignin-based biochar (Fe-LB)	MB	0.015	200	885.97	Sun et al. (2022)
Pistachio shells biochar	MB	0.03	90	21.344	Saghir et al. (2022)
Porous biochar-supported Fe-Mn composite	AR88	0.05	/	1570	Chen et al. (2020)
Composite of pecan nutshells biochar-ZnO	AR97	0.025	/	253.23	Leichtweis et al. (2020)
Eggshell membranes biochar	MB	0.025	110.38	8.484	Wu et al. (2022)
Chemically modified sugarcane bagasse-based biocomposites	AR1	0.05	143.40∼205.10	30.19	Kamran et al. (2022)
Abelmoschus esculentus seeds biochar	DB-86	1.00	277.04	146.51	Kumar and Gupta (2023)
PnsAC	DB-86	3.00	125.5	802.6	Garg et al. (2019)
PnsAC-alginate adsorbent			24.65	142.5

Conclusion

Zn-BCs obtained through pyrolysis and carbonization of ZnCl₂ modified sugar bagasse at varying temperatures (400, 500, and 600°C), can effectively adsorb MB and AR. SEM analysis revealed that Zn-BCs had a well-defined pore structure, which aided in the efficient adsorption of dyes. The analysis of adsorption isotherm and kinetics models about adsorption showed that the procedure of adsorption involved the coexistence of multiple mechanisms. Adsorption efficiency of Zn-BC-600 on MB and AR was best, and maximum adsorption capacity were 182.225 and 43.327 mg/g. Regeneration studies have shown that Zn-BCS can be regenerated efficiently and reused in multiple cycles. The results of the adsorption tests indicated that Zn-BCs could effectively treat both single dyes and synthetic dye wastewater. The porous structure, electrostatic interaction, π–π interaction, pore diffusion and hydrogen bonding of Zn-BCs facilitated the effective adsorption of MB and AR. This method can be considered a viable modification technology, providing significant information and technical support for the reuse of agricultural waste.

Footnotes

Acknowledgments

This work was supported by Public Projects of Zhejiang Province, China (no: 2015C33305) and was supported by the National Foundation of China (grant no: 42177380).

Authors’ Contributions

Wenfang Zhu: conceptualization, supervision, funding acquisition, resources, project administration, and writing–review and editing. Fangyuan Chen: conceptualization, data curation, methodology, validation, writing–original draft, and formal analysis. Lei Ye: data curation, investigation, methodology, and validation. Xinyuan Yang: supervision, writing–review and editing. Yali Song: writing–review and editing and resources. Hua Wang: supervision and writing–review and editing.

Data availability

We are willing to share the raw data if required.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Wenfang Zhu

References

Abdel-Fadeel

Aljohani

Al-Mhyawi

, et al. (2022) A simple method for removal of toxic dyes such as brilliant green and acid red from the aquatic environment using halloysite nanoclay. Journal Saudi Chemical Society 26: 101475.

Cao

Yang

Liu

, et al. (2024) Adsorption experiments and mechanisms of methylene blue on activated carbon from garden waste via deep eutectic solvents coupling KOH activation. Biomass Bioenergy 182: 107074.

Cavalcante

EHM

Candido

ICM

de Oliveira

, et al. (2022) 3-Aminopropyl-triethoxysilane-Functionalized Tannin-Rich grape biomass for the adsorption of methyl orange dye: Synthesis, characterization, and the adsorption mechanism. ACS Omega 7(22): 18997–19009.

Cazetta

Vargas

AMM

Nogami

, et al. (2011) NaOH-activated carbon of high surface area produced from coconut shell: Kinetics and equilibrium studies from the methylene blue adsorption. Chemical Engineering Journal 174: 117–125.

Chen

Jiang

Xie

, et al. (2020) A novel porous biochar-supported Fe-Mn composite as a persulfate activator for the removal of acid red 88. Seperation and Purification Technology 250: 117232.

Chen

Huang

, et al. (2022) Enhanced adsorption of phosphate on orange peel-based biochar activated by Ca/Zn composite: Adsorption efficiency and mechanisms. Colloids Surface A: Physicochemical and Engeneering Aspects 651: 129728.

Chung

(2016) Azo dyes and human health: A review. Journal Environomental Science Health C 34: 233–261.

Cruz-Olivares

Pérez-Alonso

Martínez-Barrera

, et al. (2022) Modeling and scaling up of the Cr(VI) adsorption process by using mexicalcite natural mineral in a packed bed column. Results Engineering 16: 100687.

Dai

Liu

Zhang

, et al. (2022) Synergetic effect of co-pyrolysis of sewage sludge and lignin on biochar production and adsorption of methylene blue. Fuel 324: 124587.

10.

Dai

Shan

(2020) Adsorption of tetracycline in aqueous solution by biochar derived from waste Auricularia auricula dregs. Chemosphere 238: 124432.

11.

Dawood

Sen

Phan

(2019) Performance and dynamic modelling of biochar and kaolin packed bed adsorption column for aqueous phase methylene blue (MB) dye removal. Environoenmtal Technology 40(28): 3762–3772.

12.

Dong

Jin

, et al. (2021) Enhanced adsorption of Eu(III) from wastewater using Solidago canadensis-derived biochar functionalized by Ca/Al-LDH and hydroxyapatite. Applied Surface Science 567: 150794.

13.

dos Reis

Bergna

Grimm

, et al. (2023) Preparation of highly porous nitrogen-doped biochar derived from birch tree wastes with superior dye removal performance. Colloids Surface A: Physicochemical and Engineering Aspects 669: 131493.

14.

Fahoul

Zouheir

Tanji

, et al. (2021) Synthesis of a novel ZnAl₂O₄/CuS nanocomposite and its characterization for photocatalytic degradation of acid red 1 under UV illumination. Journal of Alloy Compound 889: 161708.

15.

Garg

Majumder

Kumar

, et al. (2019) Removal of direct blue-86 dye from aqueous solution using alginate encapsulated activated carbon (PnsAC-alginate) prepared from waste peanut shell. Journal of Environomental Chemical Engineering 7(5): 103365.

16.

Heidarinejad

Rahmanian

Fazlzadeh

, et al. (2018) Enhancement of methylene blue adsorption onto activated carbon prepared from date press cake by low frequency ultrasound. Journal of Molicule Liquids 264: 591–599.

17.

Sun

Gao

, et al. (2020) Synthesis of ZnO nanoparticle-anchored biochar composites for the selective removal of perrhenate, a surrogate for pertechnetate, from radioactive effluents. Journal of Hazard Materials 387: 121670.

18.

Iwuozor

Chizitere Emenike

Ighalo

, et al. (2022) A review on the thermochemical conversion of sugarcane bagasse into biochar. Cleaner Materrials 6: 100162.

19.

Kamran

Bhatti

Noreen

, et al. (2022) Chemically modified sugarcane bagasse-based biocomposites for efficient removal of acid red 1 dye: Kinetics, isotherms, thermodynamics, and desorption studies. Chemosphere 291: 132796.

20.

Kumar

Gupta

(2023) Green synthesis of novel biochar from Abelmoschus esculentus seeds for direct blue 86 dye removal: Characterization, RSM optimization, isotherms, kinetics, and fixed bed column studies. Environmental and Pollution 337: 122559.

21.

Leichtweis

Silvestri

Carissimi

(2020) New composite of pecan nutshells biochar-ZnO for sequential removal of acid red 97 by adsorption and photocatalysis, biomass. Bioenergy 140: 105648.

22.

Leng

Yuan

Zeng

, et al. (2015) Surface characterization of rice husk bio-char produced by liquefaction and application for cationic dye (malachite green) adsorption. Fuel 155: 77–85.

23.

Liu

Chen

Wang

, et al. (2022) Enhanced removal of Cd²⁺ from water by AHP-pretreated biochar: Adsorption performance and mechanism. Journal of Hazard Materials 438: 129467.

24.

Liu

Fan

Wang

, et al. (2024) Chemical speciation distribution, desorption characteristics, and quantitative adsorption mechanisms of cadmium/lead ions adsorbed on biochars. Arabians Journal of Chemical 17(4): 105669.

25.

Liu

Zhang

, et al. (2023) Enhanced adsorption of Congo red from urea/calcium chloride co-modified biochar: Performance, mechanisms and toxicity assessment. Bioresource Technology 388: 129783.

26.

Nadeem

Munawar

Mukhtar

, et al. (2021) Enhancement in the photocatalytic and antimicrobial properties of ZnO nanoparticles by structural variations and energy bandgap tuning through Fe and Co co-doping. Ceramics International 47: 11109–11121.

27.

Nuanhchamnong

Kositkanawuth

Wantaneeyakul

(2022) Granular waterworks sludge-biochar composites: Characterization and dye removal application, results. Engineering 14: 100451.

28.

Omer

El Naeem

Abd-Elhamid

, et al. (2022) Adsorption of crystal violet and methylene blue dyes using a cellulose-based adsorbent from sugarcane bagasse: Characterization, kinetic and isotherm studies. Journal of Materials Resources and Technology 19: 3241–3254.

29.

Pap

Shearer

Gibb

(2023) Preparation and characterization of activated carbon derived from deashing coal slime with ZnC_l2 activation. Journal of Environomental Chemical Engineering 11: 110360.

30.

Pleşa Chicinaş

Bedelean

Stefan

, et al. (2018) Ability of a montmorillonitic clay to interact with cationic and anionic dyes in aqueous solutions. Journal of Molecule Structure 1154: 187–195.

31.

Saghir

, et al. (2022) Synthesis of high surface area porous biochar obtained from pistachio shells for the efficient adsorption of organic dyes from polluted water. Surfaces and Interfaces 34: 102357.

32.

Sahu

Pahi

Tripathy

, et al. (2020) Adsorption of methylene blue on chemically modified lychee seed biochar: Dynamic, equilibrium, and thermodynamic study. Journal of Molecules Liquids 315: 113743.

33.

Salama

(2018) Preparation of CMC-g-P (SPMA) super adsorbent hydrogels: Exploring their capacity for MB removal from waste water. International Journal of Biology Macromolecules 106: 940–946.

34.

Shao

Shuangbao Wu

, et al. (2024) Two-step pyrolytic preparation of biochar for the adsorption study of tetracycline in water. Environmental Research 242: 117566.

35.

Shenvi

Isloor

Ismail

, et al. (2015) Humic acid based biopolymeric membrane for effective removal of methylene blue and rhodamine B. Industrial & Engineering Chemical Research 54: 150423122803005.

36.

Sun

Jin

, et al. (2022a) Qualitative and quantitative investigation on adsorption mechanisms of Cd(II) on modified biochar derived from co-pyrolysis of straw and sodium phytate. Science of the Total Environomental 829: 154599.

37.

Sun

Wang

Han

, et al. (2022b) Facile synthesis of Fe-modified lignin-based biochar for ultra-fast adsorption of methylene blue: Selective adsorption and mechanism studies. Bioresource Technology 344: 126186.

38.

Tang

Snoussi

Bhakta

, et al. (2023) Unusual, hierarchically structured composite of sugarcane pulp bagasse biochar loaded with Cu/Ni bimetallic nanoparticles for dye removal. Journal of Environomental Research 232: 116232.

39.

Thue

Lima

, et al. (2022) Comparative studies of physicochemical and adsorptive properties of biochar materials from biomass using different zinc salts as activating agents. Journal of Environomenatl Chemical Engineering 10: 107632.

40.

Tong

Zhuang

Lee

, et al. (2019) Concurrent transport and removal of nitrate, phosphate and pesticides in low-cost metal- and carbon-based materials. Chemosphere 230: 84–91.

41.

Tsamo

Assabe

Argue

, et al. (2019) Discoloration of methylene blue and slaughter house wastewater using maize cob biochar produced using a constructed burning chamber: A comparative study. Science African 3: e00078.

42.

Usman

Khan

(2022) Selective adsorption of anionic dye from wastewater using polyethyleneimine based macroporous sponge: Batch and continuous studies. Journal of Hazard Material 428: 128238.

43.

Wang

Sun

Ren

, et al. (2017) Sorption of naphthalene and its hydroxyl substitutes onto biochars in single-solute and bi-solute systems with propranolol as the co-solute. Chemical Engineering Journal 326: 281–291.

44.

Wang

Yuan

Zeng

, et al. (2014) Removal of malachite green dye from wastewater by different organic acid-modified natural adsorbent: Kinetics, equilibriums, mechanisms, practical application, and disposal of dye-loaded adsorbent. Environmental Science and Pollution Research 21: 11552–11564.

45.

Wang

Sun

Huang

, et al. (2021a) Adsorption and thermal degradation of microplastics from aqueous solutions by Mg/Zn modified magnetic biochars. Joural of Hazard Materials 419: 126486.

46.

Wang

Yan

, et al. (2018) Microwave-assisted preparation of nitrogen-doped biochars by ammonium acetate activation for adsorption of acid red 18. Applied Surface Science 433: 222–231.

47.

Wang

Gao

Cao

, et al. (2021b) Self-propagating synthesis of Zn-loaded biochar for tetracycline droxide supported Au nanoparticles for highly efficient base-free aerobic oxidation of glucose. Science of the Total Environomental 759: 143542.

48.

Wei

Salih

KAM

Rabie

, et al. (2021) Development of phosphoryl-functionalized algal-PEI beads for the sorption of Nd(III) and Mo(VI) from aqueous solutions - application for rare earth recovery from acid leachates. Chemical Engineering Journal 412: 127399.

49.

Wolski

Sobanska

Nowaczyk

, et al. (2022) Phosphate doping as a promising approach to imp-rove reactivity of Nb₂O₅ in catalytic activation of hydrogen peroxide and removal of methylene blue via adsorption and oxidative degradation. Jouran of Hazard Material 440: 129783.

50.

Yang

Cao

, et al. (2022) Activation and adsorption mechanisms of methylene blue removal by porous biochar adsorbent derived from eggshell membrane. Chemical Engineering Research and Design 188: 330–341.

51.

Xing

Zhang

Zhou

, et al. (2023) Mechanisms of polystyrene nanoplastics adsorption onto activated carbon modified by ZnCl₂, Science of the Total Environomental 876: 162763.

52.

Yang

Zhu

Song

, et al. (2021) Removal of cationic dye BR46 by biochar prepared from Chrysanthemum morifolium Ramat straw: A study on adsorption equilibrium, kinetics and isotherm. Journal of Molecule Liquid 340: 116617.

53.

Yang

Phuong Nguyen

Van

, et al. (2022) Zno nanoparticles loaded rice husk biochar as an effective adsorbent for removing reactive red 24 from aqueous solution. Material Science in Semicon Procedure 150: 106960

54.

Tian

Zou

, et al. (2021) Zno/biochar nanocomposites via solvent free ball milling for enhanced adsorption and photocatalytic degradation of methylene blue. Journal of Hazard Material 415: 125511.

55.

Zafeer

Menezes

Venkatachalam

, et al. (2023) Sugarcane bagasse-based biochar and its potential applications: A review. Emergent Materials 7(1): 133–161.

56.

Zeng

, et al. (2019) Research on the sustainable efficacy of g-MoS₂ decorated biochar nanocomposites for removing tetracycline hydrochloride from antibiotic-polluted aqueous solution iron. Environmental Science 648: 206–217.

57.

Zhang

Yang

Jiang

, et al. (2022) Preparation and characterization of activated carbon derived from deashing coal slime with ZnCl₂ activation. Colloids and Surfaces A: Physicochemical and Engineering Aspects 641: 128124.

58.

Zheng

Pan

Zheng

, et al. (2024) Functionalized magnetic chitosan-based adsorbent for efficient tetracycline removal: Deep investigation of adsorption behaviors and mechanisms. Seperation and Purification Technology 335: 126212.

59.

Zhuge

Fan

Lin

, et al. (2024) A hybrid composite of hydroxyapatite and Ca-Al layered double hydroxide supported au nanoparticles for highly efficient base-free aerobic oxidation of glucose. Dalton Transactions 1–72.