Biochar as an Eco-Friendly and Economical Adsorbent for the Removal of Colorants (Dyes) from Aqueous Environment: A Review

A critical review on biochar for the removal of toxic pollutants from water environment

As an effort to tackle some of the most pressing ecological issues we are currently experiencing, there has been an increasing interest in employing biomass-derived char products in various disciplines. Thermal combustion of biomass results in biochar production, which is a remarkably rich source of carbon. Not only does the biochar obtained by the thermochemical breakdown of biomass lower the quantity of carbon released into the environment, but it also serves as an eco-friendly substitute for activated carbon (AC) and further carbon-containing products. An overview of using biochar to remove toxic pollutants is the main subject of this article. Several techniques for producing biochar have been explored. The most popular processes for producing biochar are hydrothermal carbonization, gasification and pyrolysis. Carbonaceous materials, alkali, acid and steam are all capable of altering biochar. Depending on the environmental domains of applications, several modification techniques are chosen. The current findings on characterization and potential applications of biochar are compiled in this survey. Comprehensive discussion is given on the fundamentals regarding the formation of biochar. Process variables influencing the yield of biochar have been summarized. Several biochars' adsorption capabilities for expulsion pollutants under various operating circumstances are compiled. In the domain of developing biochar, a few suggestions for future study have been given.

Simultaneous removal of ammonium, phosphate, and phenol via self-assembled biochar composites CBCZrOFe3O4 and its utilization as soil acidity amelioration

High concentrations of ammonium, phosphate, and phenol are recognized as water pollutants that contribute to the degradation of soil acidity. In contrast, small quantities of these nutrients are essential for soil nutrient cycling and plant growth. Here, we reported composite materials comprising biochar, chitosan, ZrO, and Fe3O4, which were employed to mitigate ammonium, phosphate, and phenol contamination in water and to lessen soil acidity. Batch adsorption experiments were conducted to assess the efficacy of the adsorbents. Initially, comparative studies on the simultaneous removal of NH4, PO4, and phenol using CB (biochar), CBC (biochar + chitosan), CBCZrO (biochar + chitosan + ZrO), and CBCZrOFe3O4 (biochar + chitosan + ZrO + Fe3O4) were conducted. The results discovered that CBCZrOFe3O4 exhibited the highest removal percentage among the adsorbents (P < 0.05). Adsorption data for CBCZrOFe3O4 were well fitted to the second-order kinetic and Freundlich isotherm models, with maximum adsorption capacities of 112.65 mg/g for NH4, 94.68 mg/g for PO4 and 112.63 mg/g for phenol. Subsequently, the effect of CBCZrOFe3O4-loaded NH4, PO4, and phenol (CBCZrOFe3O4-APP) on soil acidity was studied over a 60-day incubation period. The findings showed no significant changes (P < 0.05) in soil exchangeable acidity, H+, Mg, K, and Na. However, there was a substantial increase in the soil pH, EC, available P, CEC, N-NH4, and N-NO3. A significant reduction was also observed in the available soil exchangeable Al and Fe (P < 0.05). This technique demonstrated multi-functionality in remediating water pollutants and enhancing soil acidity.

Engineered lignocellulosic based biochar to remove endocrine-disrupting chemicals: Assessment of binding mechanism

The safety and health of aquatic organisms and humans are threatened by the increasing presence of pollutants in the environment. Endocrine disrupting chemicals are common pollutants which affect the function of endocrine and causes adverse effects on human health. These chemicals can disrupt metabolic processes by interacting with hormone receptors upon consumptions by humans or aquatic species. Several studies have reported the presence of endocrine disrupting chemicals in waterbodies, food, air and soil. These chemicals are associated with increasing occurrence of obesity, metabolic disorders, reproductive abnormalities, autism, cancer, epigenetic variation and cardiovascular risk. Conventional treatment processes are expensive, not environment friendly and unable to achieve complete removal of these harmful chemicals. In recent years, biochar from different sources has gained a considerable interest due to their adsorption efficiency with porous structure and large surface areas. biochar derived from lignocellulosic biomass are widely used as sustainable catalysts in soil remediation, carbon sequestration, removal of organic and inorganic pollutants and wastewater treatment. This review conceptualizes the production techniques of biochar from lignocellulosic biomass and explores the functionalization and interaction of biochar with endocrine-disrupting chemicals. This review also identifies the further needs of research. Overall, the environmental and health risks of endocrine-disrupting chemicals can be dealt with by biochar produced from lignocellulosic biomass as a sustainable and prominent approach.

Adsorption of Pb, Cu, and Ni Ions on Activated Carbon Prepared from Oak Cupules: Kinetics and Thermodynamics Studies

Agricultural residue-activated carbon and biochar, inexpensive and environmentally friendly adsorbent materials, have recently received significant research attention. This study investigated the potential use of oak cupules in activated carbon form to remove widespread heavy metals (Pb2+, Cu2+, and Ni2+) from wastewater. The oak-activated carbon was prepared from oak cupules and activated with phosphoric acid. Oak-activated carbon was characterized using FTIR, BET analysis, energy-dispersive X-ray spectrometry (EDS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Freundlich, Langmuir, and Temkin isotherm models were used to assess the equilibrium data. The impact of various parameters, including pH effect, temperature, adsorbent dose, and contact time, was estimated. The Freundlich model was the most agreeable with Pb2+ adsorption by oak-based activated carbon, and Langmuir was more compatible with Cu2+ and Ni2+. Under optimum conditions, the average maximum removal was 63% Pb2+, 60% Cu2+, and 54% Ni2+ when every ion was alone in the aqueous solution. The removal was enhanced to 98% Pb2+, 72% Cu2+, and 60% Ni2+ when found as a mixture. The thermodynamic model revealed that the adsorption of ions by oak-based activated carbon is endothermic. The pseudo-second-order kinetic best describes the adsorption mechanism in this study; it verifies chemical sorption as the rate-limiting step in adsorption mechanisms. The oak-activated carbon was effective in removing Pb2+, Cu2+, and Ni2+ from wastewater and aqueous solutions.

Hymenaea courbaril resin-mediated gold nanoparticles as catalysts in organic dyes degradation and sensors in pharmaceutical pollutants

In this study, green synthesis of gold nanoparticles (AuNPs) using aqueous extract from Hymenaea courbaril resin (HCR) is reported. The successful formation, functional group involvement, size, and morphology of the subject H. courbaril resin mediated gold nanoparticles (HCRAuNPs) were confirmed by Ultra Violet-Visible (UV-vis) spectroscopy, Fourier-Transform Infrared spectroscopy (FTIR), and Transmission Electron Microscopy (TEM) techniques. Stable and high yield of HCRAuNPs was formed in 1:15 (aqueous solution: salt solution) reacted in sunlight as indicated by the visual colour change and appearance of surface Plasmon resonance (SPR) at 560 nm. From the FT-IR results, the phenolic hydroxyl (-OH) functional group was found to be involved in synthesis and stabilization of nanoparticles. The TEM analysis showed that the particles are highly dispersed and spherical in shape with average size of 17.5 nm. The synthesized HCRAuNPs showed significant degradation potential against organic dyes, including methylene blue (MB, 85 %), methyl orange (MO, 90 %), congo red (CR, 83 %), and para nitrophenol (PNP, 76 %) up to 180 min. The nanoparticles also demonstrated the effective detection of pharmaceutical pollutants, including amoxicillin, levofloxacin, and azithromycin in aqueous environment as observable changes in color and UV-Vis spectral graph.

Conversion of locally available materials to biochar and activated carbon for drinking water treatment

For environmental sustainability and to achieve sustainable development goals (SDGs), drinking water treatment must be done at a reasonable cost with minimal environmental impact. Therefore, treating contaminated drinking water requires materials and approaches that are inexpensive, produced locally, and effortlessly. Hence, locally available materials and their derivatives, such as biochar (BC) and activated carbon (AC) were investigated thoroughly. Several researchers and their findings show that the application of locally accessible materials and their derivatives are capable of the adsorptive removal of organic and inorganic contaminants from drinking water. The application of locally available materials such as lignocellulosic materials/waste and its thermo-chemically derived products, including BC and AC were found effective in the treatment of contaminated drinking water. Thus, this review aims to thoroughly examine the latest developments in the use of locally accessible feedstocks for tailoring BC and AC, as well as their features and applications in the treatment of drinking water. We attempted to explain facts related to the potential mechanisms of BC and AC, such as complexation, co-precipitation, electrostatic interaction, and ion exchange to treat water, thereby achieving a risk-free remediation approach to polluted water. Additionally, this research offers guidance on creating efficient household treatment units based on the health risks associated with customized adsorbents and cost-benefit analyses. Lastly, this review work discusses the current obstacles for using locally accessible materials and their thermo-chemically produced by-products to purify drinking water, as well as the necessity for technological interventions.

Actas Pink-2B dye removal in biochar nanocomposites augmented vertical flow constructed wetland (VF-CWs)

Industries generate hazardous dye wastewater, posing significant threats to public health and the environment. Removing dyes before discharge is crucial. The ongoing study primarily focused on synthesizing, applying, and understanding the mechanism of green nano-biochar composites. These composites, including zinc oxide/biochar, copper oxide/biochar, magnesium oxide/biochar, and manganese oxide/biochar, are designed to effectively remove Actas Pink-2B (Direct Red-31) in conjunction with constructed wetlands. Constructed wetland maintained pH 6.0-7.9. At the 10th week, the copper oxide/biochar treatment demonstrated the highest removal efficiency of total suspended solids (72%), dissolved oxygen (7.2 mg/L), and total dissolved solids (79.90%), followed by other biochar composites. The maximum removal efficiency for chemical oxygen demand (COD) and color was observed at a retention time of 60 days. The electrical conductivity also followed the same order, with a decrease observed up to the 8th week before becoming constant. A comprehensive statistical analysis was conducted, encompassing various techniques including variance analysis, regression analysis, correlation analysis, and principal component analysis. The rate of color and COD removal followed a second-order and first-order kinetics, respectively. A significant negative relationship was observed between dissolved oxygen and COD. The study indicates that employing biochar composites in constructed wetlands improves textile dye removal efficiency.

Facile synthesis and ultrastrong adsorption of a novel polyacrylamide-modified diatomite/cerium alginate hybrid aerogel for anionic dyes from aqueous environment

An eco-friendly cationic polyacrylamide (CPAM)-modified diatomite/Ce(III)-crosslinked sodium alginate hybrid aerogel (CPAM-Dia/Ce-SA) was synthesized successfully and characterized by SEM-EDS, XRD, FTIR, UV-Vis and XPS. Adsorption performance, interaction mechanism and reusability of CPAM-Dia/Ce-SA used for the removal of acid blue 113 (AB 113), acid blue 80 (AB 80), acid yellow 117 (AY 117), Congo red (CR) and Direct Green 6 (DG 6) anionic dyes from aqueous media were investigated in detail. The results demonstrate that CPAM-Dia/Ce-SA aerogel is macroscopic polymer hybrid spheres with a particle size of around 1.3 mm, unique undulating mountain-like surface and porous mesostructure, and exhibits outstanding adsorption capacity for anionic dyes and good reusability. The maximum adsorption amounts of AB 113, AB 80, AY 117, CR and DG 6 by CPAM-Dia/Ce-SA were 3008, 1208, 914, 1832 and 1232 mg/g at pH 2.0, 60 min contact time and 25 °C, and corresponding removal efficiency reached individually 97.5, 96.6, 99.7, 99.9 and 98.5 % respectively and were less affected by increasing pH up to 10.0. Dye adsorption behaviour and adsorption processes with spontaneous and exothermic nature were perfectly interpreted by the Langmuir and Pseudo-second-order rate models respectively. Physicochemical and multisite-H-bonding synergies promoted the ultrastrong biosorption of anionic dyes by CPAM-Dia/Ce-SA.

Straw-derived biochar for the removal of antibiotics from water: Adsorption and degradation mechanisms, recent advancements and challenges

Antibiotics, a kind of containments with the properties of widely distributed and difficult to degrade, has aroused extensive attention in the world. As a prevalent agricultural waste, straws can be utilized to prepare biochar (straw-derived biochar, SBC) to remove antibiotics from aquatic environment. To date, although a number of review papers have summarized and discussed research on biochar application in wastewater treatment and soil remediation, there are few reviews on SBC for antibiotic removal. Due to the limitations of poor adsorption and degradation performance of the pristine SBC, it is necessary to modify SBC to improve its applications for antibiotics removal. The maximum antibiotic removal capacity of modified SBC could reach 1346.55 mg/g. Moreover, the adsorption mechanisms between modified SBC and antibiotics mainly involve π-π interactions, electrostatic interactions, hydrophobic interactions, and charge dipole interactions. In addition, the modified SBC could completely degrade antibiotics within 6 min by activating oxidants, such as PS, PDS, H2O2, and O3. The mechanisms of antibiotic degradation by SBC activated oxidants mainly include free radicals (including SO4•-, •OH, and O2•-) and non-free radical pathway (such as, 1O2, electrons transfer, and surface-confined reaction). Although SBC and modified SBC have demonstrated excellent performance in removing antibiotics, they still face some challenges in practical applications, such as poor stability, high cost, and difficulties in recycling. Therefore, the further research directions and trends for the development of SBC and biochar-based materials should be taken into consideration.

Efficient removal of both heavy metal ion and dyes from wastewater using magnetic response adsorbent of block polymer brush-grafted N-doped biochar

The recovery of biomass from agricultural and forestry waste could realize effective utilization of waste and synthesis of novel adsorbent. Herein, porous biochar was prepared from waste ginkgo biloba leaves and modified by Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT). And the prepared adsorbent exhibited excellent adsorption capacity owing to its abundant functional groups and porous structure. In addition, the adsorption capacities of the prepared adsorbent for Malachite Green (MG), Amaranth (AM) and Cr (Ⅵ) were 422.59, 373.75 and 368.82 mg/g, respectively, surpassing those of many previously reported materials. Subsequently, the influence of various factors on adsorption performance was studied. The results showed that adsorption of MG, AM and Cr (Ⅵ) on adsorbent followed pseudo-second-order and Langmuir models and the adsorbent also displayed excellent cycling performance. The experimental results of application in various water samples showed that the adsorbent had outstanding adsorption performance in real water samples, further proving that the adsorbent had wide application and practicability. Finally, a simple adsorption column was used for filtration experiments to simulate industrial application. The results were exhibited that the adsorbent had great potential in treating wastewater containing MG, AM and Cr (Ⅵ).

Potential Environmental Contaminants: Exploring Hydrolyzed Dyes in Household Washing Sources and Electrochemical Degradation

Reactive dyes are often released into the environment during the washing process due to their susceptibility to hydrolysis. The hydrolysis experiment of a pure reactive dye, red 195 (RR 195), and the washing experiment of RR 195-colored fabrics (CFSCs) were carried out successively to explore the sources of hydrolyzed dyes in the washing microenvironment. Reversed-phase high-performance liquid chromatography (RP-HPLC) was used for the analysis of hydrolysis intermediates and final products of reactive red 195. The experimental results indicated that the structure of the dye washing shed is consistent with the final hydrolysate of reactive red 195, which is the main colored contaminant in washing wastewater. To eliminate the hydrolyzed dyes from the source, an electrochemical degradation device was designed. The degradation parameters, including voltage, electrolyte concentration, and dye shedding concentration are discussed in the electrochemical degradation experiment. The electrochemical degradation device was also successfully implemented and verified in a home washing machine.

Systematic studies on the effect of structural modification of orange peel for remediation of phenol contaminated water

In the present study, orange peel biochar has been utilized as the adsorbent for the removal of phenol from contaminated water. The biochar was prepared by thermal activation process at three different temperature 300, 500 and 700°C and are defined as B300, B500, and B700 respectively. The synthesized biochar has been characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), RAMAN spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy. SEM analysis revealed a highly irregular and porous structure for B700 as compared with others. The parameters such as initial phenol concentration, pH, adsorption dosage, and contact time were optimized, and the maximum adsorption efficiency and capacity of about 99.2% and 31.0 mg/g was achieved for B700 for phenol adsorption. The Branauer-Emmett-Teller (BET) surface area and Berrate-Joyner-Halenda (BJH) pore diameter obtained for B700 were about 67.5 m² /g and 3.8 nm. The adsorption of phenol onto the biochar followed Langmuir isotherm showing linear fit with R²  = 0.99, indicating monolayer adsorption. The kinetic data for adsorption is best fitted for pseudo-second order. The thermodynamic parameters ΔG°, ΔH°, and ΔS° values obtained are negative, which means that the adsorption process is spontaneous and exothermic. The adsorption efficiency of phenol marginally declined from 99.2% to 50.12% after five consecutive reuse cycles. The study shows that the high-temperature activation increased the porosity and number of active sites over the orange peel biochar for efficient adsorption of phenol. PRACTITIONER POINTS: Orange peel is thermally activated at 300, 500, and 700°C for structure modification. Orange peel biochars were characterized for its structure, morphology, functional groups, and adsorption behavior. High-temperature activation improved the adsorption efficiency up to 99.21% due to high porosity.

Cationic modification of cellulose as a sustainable and recyclable adsorbent for anionic dyes

There is a dire need to find an efficient, cost-effective, sustainable, and environment-friendly adsorbent for the removal of anionic pollutants such as dyes from waste effluent. In this work, a cellulose-based cationic adsorbent was designed and utilized for methyl orange and reactive black 5 anionic dyes adsorption from an aqueous medium. Solid-state nuclear magnetic resonance spectroscopy (NMR) revealed the successful modification of cellulose fibers, and dynamic light scattering (DLS) evaluations showed the levels of charge densities. Furthermore, various models for adsorption equilibrium isotherm were utilized to understand the adsorbent characteristics, with the Freundlich isotherm model providing an excellent fit for the experimental results. The modelled maximum adsorption capacity was as much as 1010 mg/g for both model dyes. The dye adsorption was also confirmed using EDX. It was noted that the dyes were chemically adsorbed through the ionic interaction that can be reversed using sodium chloride solution. Overall, the cationized cellulose is inexpensive, environment-friendly, nature-driven, and recyclable making it an appealing adsorbent feasible for the dye removal from textile wastewater effluent.

Methylene blue removal from aqueous solutions using a biochar/gellan gum hydrogel composite: Effect of agitation mode on sorption kinetics

Hydrogel membranes are prepared by casting a mixture of gellan gum (associated with PVA) and biochar produced from a local Egyptian plant. The mesoporous material is characterized by a specific surface area close to 134 m² g^-1, a residue of 28 % (at 800 °C), and a pH_PZC close to 6.43. After grinding, the material is tested for Methylene Blue sorption at pH 10.5: sorption capacity reaches 1.70 mmol MB g^-1 (synergistic effect of the precursors). The sorption isotherms are fitted by both Langmuir and Sips eqs. MB sorption increases with temperature: the sorption is endothermic (∆H°: 12.9 kJ mol^-1), with positive entropy (∆S°: 125 J mol^-1 K^-1). Uptake kinetics are controlled by agitation speed (optimum ≈200 rpm) and resistance to intraparticle diffusion. The profiles are strongly affected by the mode of agitation: the equilibrium time (≈180 min) is reduced to 20-30 min under sonication (especially at frequency: 80 kHz). The mode of agitation controls the best fitting equation: pseudo-first order rate agitation for mechanical agitation contrary to pseudo-second order rate under sonication. The sorption of MB is poorly affected by ionic strength (loss <6 % in 45 g L^-1 NaCl solution). Desorption (faster than sorption) is completely achieved using 0.7 M HCl solution. At the sixth recycling, the loss in sorption is close to 5 % (≈ decrease in desorption efficiency). The process is successfully applied for the treatment of MB-spiked industrial solution: the color index decreases by >97 % with a sorbent dose close to 1 g L^-1; a higher dose is required for maximum reduction of the COD (60 % at 3 g L^-1).

Removal of Methylene Blue from Aqueous Solution by Mixture of Reused Silica Gel Desiccant and Natural Sand or Eggshell Waste

The purpose of this work was to develop, characterize and test new low-cost materials suitable for removing methylene blue dye from water and wastewater by adsorption. The solid materials consisted of silica gel powder (SG), silica gel mixed with eggshell powder (SG-ES) and a mixture of silica gel with sand from the western Iraqi desert (SG-SI). The samples were milled by using an electrical mixer and a ball mill, followed by a drying step. In addition, desert sand was acid-treated in order to remove impurities. The structure and chemical composition of the samples were investigated by X-ray diffraction (XRD), a scanning electron microscopy technique equipped with an energy-dispersive X-ray spectrometer (SEM-EDX), a low-temperature nitrogen adsorption (BET) technique, thermo-analytical (TG/TGA) measurements and Fourier-transformed infrared spectroscopy (FTIR). The previously mentioned materials were tested to remove methylene blue from an aqueous solution. The adsorption experiments were monitored by ultraviolet-visible (UV-Vis) spectrophotometry and showed that SG and SG-ES gave promising results for the methylene blue removal from water. After 40 min of treatment of the aqueous solution containing 10 mg/L of MB at room temperature, the tested SG, SG-ES and SG-SI materials were found to have 86%, 80% and 57% dye adsorption efficiency, respectively. Taking into consideration not only the adsorption activity of the studied material but their availability, cost and concepts of cleaner production and waste minimization, the developed silica gel with eggshell can be considered as a good, cost-effective alternative to commercially available activated-carbon-based adsorbents. Different kinetic and isotherm models were fitted to the experimental results. A pseudo-second-kinetics-order model revealed high correlation fitting, while the Freundlich model was found to appropriately describe the adsorption isotherm. The thermal stability during the possible regeneration process of the SG-ES adsorbent mixture and its interaction mechanism with cationic dye was discussed.

Biochar as Sustainable Alternative and Green Adsorbent for the Remediation of Noxious Pollutants: A Comprehensive Review

The current water crisis necessitates the development of new materials for wastewater treatment. A variety of nanomaterials are continuously being investigated for their potential as adsorbents for environmental remediation. Researchers intend to develop a low-cost, simple, and sustainable material that can cater to removal of pollutants. Biochar derived from biowaste is a potential candidate for the existing problem of water pollution. The review focuses on the various aspects of biochar, such as its sources, preparation methods, mechanism, applications for wastewater treatment, and its regeneration. Compared with other adsorbents, biochar is considered as an environmentally friendly, sustainable, and cost-effective substitute for waste management, climate protection, soil improvement, wastewater treatment, etc. The special properties of biochar such as porosity, surface area, surface charge, and functional groups can be easily modified by various chemical methods, resulting in improved adsorption properties. Therefore, in view of the increasing environmental pollution and the problems encountered by researchers in treating pollutants, biochar is of great importance. This review also highlights the challenges and prospective areas that can be explored and studied in more detail in the future.

Macroporous Aerogels Using High Internal Phase Pickering Emulsions for Adsorption of Dyes

The treatment of industrial printing and dyeing wastewater is the focus of the chemical environmental protection industry. Noticeably, the physical adsorption has attracted wide attention due to the selective dye adsorption, simple process, and convenient operation. New aerogels featuring low density and high porosity are regarded as ideal physical adsorption materials for sewage treatment. In this work, high internal phase Pickering emulsions were designed and prepared. The polysaccharide complex originating from sodium octenylsuccinate starch and chitosan serves as the stabilizer, water and hexane act as the external and internal phase, respectively. Acrylic acid was introduced into the external phase to initiate UV polymerization. The high internal phase Pickering emulsions as templates were removed through freeze-drying to produce aerogel materials with macroporous structures, the size of the pores: 43.54 ± 12.75 μm. The scanning electron microscopy (SEM) images show that the pore size of aerogel materials was similar to that of emulsion droplets, verifying the template role of emulsion in the polymerization process. In addition, aerogels possess good mechanical properties and can withstand a pressure of megapascal, exhibiting favorable stability when floating in water for a long time (6 months). Methyl violet, malachite green, methylene blue, and acridine orange in aqueous solution were selected as model dyes to explore the removal process and the mechanism. The adsorption was conformed to be the pseudo-second-order kinetic model and the Freundlich adsorption isotherm, namely, the dye adsorption of the aerogels was the multilayer adsorption on the uneven surface, and the mechanism of the adsorption was related to the π-π interaction.

Biochar-mediated removal of pharmaceutical compounds from aqueous matrices via adsorption

Pharmaceutical is one of the noteworthy classes of emerging contaminants. These biologically active compounds pose a range of deleterious impacts on human health and the environment. This is attributed to their refractory behavior, poor biodegradability, and pseudopersistent nature. Their large-scale production by pharmaceutical industries and subsequent widespread utilization in hospitals, community health centers, and veterinary facilities, among others, have significantly increased the occurrence of pharmaceutical residues in various environmental compartments. Several technologies are currently being evaluated to eliminate pharmaceutical compounds (PCs) from aqueous environments. Among them, adsorption appears as the most viable treatment option because of its operational simplicity and low cost. Intensive research and development efforts are, therefore, currently underway to develop inexpensive adsorbents for the effective abatement of PCs. Although numerous adsorbents have been investigated for the removal of PCs in recent years, biochar-based adsorbents have garnered tremendous scientific attention to eliminate PCs from aqueous matrices because of their decent specific surface area, tunable surface chemistry, scalable production, and environmentally benign nature. This review, therefore, attempts to provide an overview of the latest progress in the application of biochar for the removal of PCs from wastewater. Additionally, the fundamental knowledge gaps in the domain knowledge are identified and novel strategic research guidelines are laid out to make further advances in this promising approach towards sustainable development.

Exploring the promising potential of fallen bamboo leaves (Bambusa bambos) for efficient removal of crystal violet from wastewater

Fallen bamboo leaves (Bambusa bambos), hereinafter BL have been designed to be transformed into an efficient and sustainable adsorbent for the removal of crystal violet (CV) dye from wastewater with up to 95% scavenging ability. BL have been characterized by Fourier transform infrared (FTIR) spectra, field emission scanning electron microscopy (FESEM), and zero point charge (pHzpc). The maximum adsorption capacity is 30 mg/g at pH 10. Physico-chemical parameters have been investigated concerning pH, contact time, initial concentration, and coexistent ions. Pseudo-second-order kinetics is followed best (R² =0.999) signifying a chemisorption pathway. Besides, intra-particle diffusion plays a governing role in the film diffusion of crystal violet into the core of the adsorbent. Langmuir isotherm model fits best (R²=0.972) suggesting a uniform, monolayer, and homogeneous adsorption. Regeneration was successful with methanol (65%) and reusability was tested for three cycles and was found to retain activity up to 80%. Analysis of CV containing industrial effluent suggests that a 36.8% reduction is possible with BL. The effect of co-existent ions suggests little influence on the adsorption. Compared to other contemporary and relevant adsorbents, it can be concluded that BL can be exercised for the sustainable decontamination of CV-containing wastewater.

Fabrication and characterization of a novel Ba2+-loaded sawdust biochar doped with iron oxide for the super-adsorption of SO42- from wastewater

Biochar is a low-cost adsorbent used in the treatment of contaminated wastewater. We investigated the potential of an Fe-impregnated, Ba²⁺-loaded biochar (Fe-(Ba-BC)) for the removal of SO₄^2- from aqueous solutions. The Ba²⁺-loaded biochar was synthesized from sawdust impregnated with iron oxide via pyrolysis at 600 °C. The porous structure of the Fe-(Ba-BC) was identified by scanning electron microscopy before sulfate was adsorbed onto the adsorbent. Functional groups were determined by energy-dispersive spectrophotometry and Raman spectrometry.. The Fe-(Ba-BC) Raman peaks before the experiment were higher than after, suggesting the precipitation of BaSO₄. The presence of BaCl₂ on the surface of the biochar was confirmed by X-ray diffraction. Batch sorption results showed that Fe-(Ba-BC) strongly adsorbed aqueous SO₄^2- with a removal efficacy of 96.7% under the optimum conditions of 0.25 M BaCl₂, a contact time of 480 min, a pH of 9 and an adsorbent dose of 2 g. The optimum condition for removal and reaction rate kinetics analysis indicated that adsorption curve fitted well with PSO, k₂ 0.00015 confirmed the removal of SO₄^2- via chemisorption. Thus, Fe-(Ba-BC) was found to be a favorable adsorbent for removing SO₄^2-.

Synthesis and Micromechanistic Studies of Sensitized Bentonite for Methyl Orange and Rhodamine-B Adsorption from Wastewater: Experimental and DFT-Based Analysis

This work reports the formation of a novel adsorbent, prepared by activating bentonite with cinnamic acid, which is highly efficient to remove dyes from wastewater. The adsorption efficiency of the cinnamic acid activated bentonite was compared with unmodified bentonite by removing methyl orange and rhodamine-B from polluted water. The characterization was performed through X-ray diffraction (XRD) Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The results indicated that acidic pH and low temperature were more suitable for the selected dyes adsorption. The analysis of the data was done by the Langmuir and Freundlich isotherms; the Freundlich isotherm showed more suitability for the equilibrium data. The data were further analyzed by pseudo-first and pseudo-second-order models to study adsorption kinetics. The results showed that methyl orange and rhodamine-B adsorption obeyed pseudo-order kinetics. The results obtained from this research suggested that acid activation of bentonite with cinnamic acid increased the surface area of the clay and hence enhanced its adsorption efficiency. The maximum adsorption efficiency for the removal of methyl orange and rhodamine-B was up to 99.3 mg g⁻¹ and 44.7 mg g⁻¹, respectively, at 25 °C. This research provides an economical modification technique of bentonite, which makes it cost-effective and a good adsorbent for wastewater treatment.

Conversion of Industrial Sludge into Activated Biochar for Effective Cationic Dye Removal: Characterization and Adsorption Properties Assessment

This paper presents an in-depth characterization of a raw industrial sludge (IS-R) and its KOH-activated biochar pyrolyzed at 750 °C (IS-KOH-B) followed by their application to remove a cationic dye from aqueous solution. Materials characterization shows that compared to the IS-R, the IS-KOH-B has improved structural, textural, and surface chemical properties. In particular, the IS-KOH-B’s BET surface area and total pore volume are about 78 and 6 times higher than those found for the IS-R, respectively. The activated biochar efficiently retained the cationic dye under wide experimental conditions. Indeed, for an initial dye concentration of 50 mg L−1, removal yields were assessed to be more than 92.5%, 93.5%, and 97.8% for a large pH range (4–10), in the presence of high contents of competing cations (3000 mg L−1 of Ca2+, Mg2+, Na+, and K+), and a low used adsorbent dose (1 g L−1), respectively. The Langmuir’s adsorption capacities were 48.5 and 65.9 mg g−1 for of IS-R and IS-KOH-B, respectively, which are higher than those reported for various adsorbents in the literature. The dye removal was found to be monolayer, spontaneous, and endothermic for both the adsorbents. Moreover, this removal process seems to be controlled by chemical reactions for IS-KOH-B whereas by both physico–chemical reactions for IS-R. This study demonstrates that the raw industrial sludge and especially its KOH-activated derived biochar could be considered as promising adsorbents for the removal of dyes from aqueous solutions.

Adsorption for rhodamine b dye and biological activity of nano-porous chitosan from shrimp shells

The present work aims to evaluate the removal capacity of Rhodamine B dye (RhB) using nano-porous chitosan (NC) from shrimp shells. NC was characterized by XRD, SEM-EDS, N2 porosimetry, zeta potential (ZP), FTIR, DLS, and zero charge point (pHZCP). Compound central rotational design (CCRD) was used to determine the ideal condition and antimicrobial activity was evaluated against different strains. NC showed characteristic of semi-crystalline material with negative charge surface (around - 21.13 mV), and SBET = 1.12 m2 g-1, Vp = 0.0064 cm3 g-1, Dp = 32.09 nm and pHZCP ≈ 7.98. Kinetic adsorption showed the pseudo first-order model had the best fit, with adsorption capacity (q1) between 3.78 and 64.43 mg g-1 and pseudo first-order kinetic constant (k1) between 0.066 and 0.052 min-1. Sips model best described the equilibrium data, with a maximum adsorption capacity of 505.131 mg g-1. Antimicrobial activity was observed at 0.25 mg mL-1 for different strains. Therefore, NC has potential application in the removal of the dye, combining sustainable development associated with nanotechnology.

Adsorptive and photocatalytic remediation of hazardous organic chemical pollutants in aqueous medium: A review

The provision of clean water is still a major challenge in developing parts of the world, as emphasized by the United Nation Sustainable Development Goals (SDG 6), and has remained a subject of extensive research globally. Advancements in science and industry have resulted in a massive surge in the amount of industrial chemicals produced within the last few decades. Persistent and emerging organic pollutants are detected in aquatic environments, and conventional wastewater treatment plants have ineffectively handled these trace, bioaccumulative and toxic compounds. Therefore, we have conducted an extensive bibliometric analysis of different materials utilized to combat organic pollutants via adsorption and photocatalysis. The classes of pollutants, material synthesis, mechanisms of interaction, merits, and challenges were comprehensively discussed. The paper highlights the advantages of various materials used in the removal of hazardous pollutants from wastewater with activated carbon having the highest adsorption capacity. Dyes, pharmaceuticals, endocrine-disrupting chemicals, pesticides and other recalcitrant organic pollutants have been successfully removed at high degradation efficiencies through the photocatalytic process. The photocatalytic degradation and adsorption processes were compared by considering factors such as cost, efficiency, ease of application and reusability. This review will be good resource material for water treatment professionals/scientists, who may be interested in adsorptive and photocatalytic remediation of organic chemicals pollutants.

A Facile Review on the Sorption of Heavy Metals and Dyes Using Bionanocomposites

Presently, hazardous metal and dye removal from wastewater is one of the major areas of research focus. For the elimination of these contaminants, many approaches have been devised and applied. However, the accomplishment of various water treatment processes has largely depended on the medium utilized and the associated problem with the leaching of harmful compounds into the water process with most commercial and chemically manufactured materials for water treatment processes. Hence, this study is aimed at reviewing existing studies on the sorption of heavy metals (HMs) and dyes using bionanocomposites (BNCs). The key focus of this review is on the development of eco-friendly, effective, and appropriate nanoadsorbents that could accomplish superior and enhanced contaminant sequestration using BNCs owing to their biodegradability, biocompatible, environmentally friendly, and not posing as secondary waste to the environment. The sorption of most pollutants was observed to be pH, sorbent dosage, and initial contaminant concentration-dependent, with most contaminants’ elimination taking place in the pH range of 2-10. The sorption process of HMs and dyes to various BNCs was superlatively depicted utilizing the Langmuir (LNR) and Freundlich (FL) as well as the pseudo-second-order (PSO) models, suggestive of the sorption process of a monolayer and multilayer and the chemisorption process, the rate-limiting stage in surface sorption. The established sorption capacities for the reviewed sorption process for various contaminants ranged from 1.47 to 740.97 mg/g. Future prospective for the treatment and remediation of contaminated water using BNCs was also discussed.

Engineered mesoporous biochar derived from rice husk for efficient removal of malachite green from wastewaters

Extremely soluble Malachite green (MG) acts as potential carcinogen for aquatic life in polluted aqueous environments. Current study aims to modify rice husk derived biochar to improve its removal efficiency for MG from MG-containing wastewaters. The hydrothermal alkali activation was effective for preparing modified biochar (RHMB) from native biochar (RHB) derived from rice husk. After modification, surface area and pore volume of RHMB was determined respectively 434.62 m²g^-1 and 287.28 cm³g^-1, significantly improved from native RHB values 21.764 m²g^-1 and 65.53 cm³g^-1. Pseudo second order kinetic model fitted well. RHMB exhibits an equilibrium adsorption capacity of 373.02 mg g^-1. RHMB showed an excellent MG removal ability and was not susceptible to ion interference even at highly saline environments. It has exhibited 96.96 ± 1.17% removal efficiency of MG and is expected to be used as potential adsorbent for MG remediation from aquaculture wastewater and other MG containing industrial wastewaters.

Attempts to alleviate inhibitory factors of anaerobic digestate for enhanced microalgae cultivation and nutrients removal: A review

Anaerobic digestion is a well-established process that is applied to treat organic wastes and convert the carbon to valuable methane gas as a source of energy. The digestate that comes out as a by-product is of a great challenge due to its high nutrient content that can be toxic in case of improper disposal to the environment. Several attempts have been done to valorize this digestate. Digestate has been considered as an interesting medium to cultivate microalgae. The nutrients available in the digestate, mainly nitrogen and phosphorus, can be an interesting supplement for microalgae growth requirement. The main obstacles of using digestate as a medium to cultivate microalgae are the dark color and the high ammonium-nitrogen concentration. The focus of this review is to discuss in detail the major attempts in research to overcome inhibition and enhance microalgae cultivation in digestate. This review initially discussed the obstacles of digestate as a medium for microalgae cultivation. Different processes to overcome inhibition were discussed including dilution, supplying additional carbon source, favoring mixotrophic cultivation and pretreatment. More emphasis in this review was given to digestate pretreatment. Among the pretreatment methods, filtration, and centrifugation were of the most applied ones. These strategies were found to be effective for turbidity and chromaticity reduction. For ammonium nitrogen removal, ammonia stripping and biological pretreatment methods were found to play a vital role. Adsorption could work both ways depending on the material used. Combining different pretreatment methods as well as including selected microalgae stains were found interesting strategies to facilitate microalgae cultivation with no dilution. This study recommend that more study should investigate the optimization of microalgae cultivation in anaerobic digestate without the need for dilution.

Dynamic Adsorption Characteristics of Phosphorus Using MBCQ

Biochar is a new type of adsorption material with excellent performance, but it has some problems, such as light texture, poor sedimentation, and difficult recovery, which limits its practical application. In this study, biochar microspheres (MBCQ) were prepared by the sol–gel method using powdery biochar from Hydrocotyle vulgaris as raw material and sodium alginate as a granular carrier. Experiments were performed to investigate the dynamic adsorption characteristics of phosphorus by MBCQ in the adsorption column and the influences of particle size, initial phosphorus concentration, flow rate, and column height on the breakthrough curve. The results showed that the static adsorption properties of different particles varied and that 3-millimeter particles were optimal. The breakthrough time positively correlated with column height and negatively correlated with initial phosphorus concentration, flow rate, and particle size. Flow velocity significantly impacted breakthrough time and length of mass transfer. The bed depth/service time model accurately predicted the relationship between breakthrough times and column heights. When ct/c0 = 0.6, the average relative deviation between predicted and measured values was the lowest. The Thomas model described the MBCQ adsorption process of Ph (R2 > 0.95), which indicated that diffusion in MBCQ adsorption was not a rate-limiting step.

Surface Hydrophobic Modification of Biochar by Silane Coupling Agent KH-570

Biochar-amended soil cover (BSC) in landfills can improve the oxidation of methane. However, adding biochar can cause a larger amount of rainwater to enter the soil cover and landfill because it increases the permeability of the soil cover, which increases leachate production. Improving the hydrophobicity and waterproof ability of BSC is expected to reduce rainwater that goes into landfills. Silane coupling agent KH-570 is used to modify biochar to improve its hydrophobicity and waterproof ability after being added to the soil cover. The waterproofness of hydrophobic biochar-amended soil cover (HBSC) was studied by conducting a precipitation simulation test. Results showed that the optimum hydrophobicity of the surface-modified biochar was obtained when the mass fraction of KH-570 was 7%, the biochar dosage was 7 g, and the modification temperature was 60 °C. In these conditions, the contact angle was 143.99° and the moisture absorption rate was 0.10%. The analysis results of thermogravimetric, X-ray diffractometer and scanning electron microscopy before and after the biochar modification showed that KH-570 formed a hydrophobic organic coating layer on the biochar surface, indicating that the surface hydrophobic modification of biochar was successfully carried out by silane coupling agent. The waterproof ability of HBSC was significantly better than that of BSC in the simulated precipitation test.

Rice Straw Biochar and Magnetic Rice Straw Biochar for Safranin O Adsorption from Aqueous Solution

This study investigates the adsorption of Safranin O (SO) from aqueous solution by both biochar and magnetic biochar derived from rice straw. Rice straw biochar (RSB) was made by pyrolysis in a furnace at 500 °C, using a heating rate of 10 °C·min−1 for 2 h in an oxygen-limited environment, whilst the magnetic rice straw biochar (MRSB) was produced via the chemical precipitation of Fe2+ and Fe3+. The physicochemical properties of the synthesized biochars were characterized using SEM, SEM- EDX, XRD, FTIR techniques, and N2 adsorption (77 K) and pHpzc measurements. Batch adsorption experiments were used to explore the effect of pH, biochar dosage, kinetics, and isotherms on the adsorption of SO. Experimental data of RSB and MRSB fit well into both Langmuir and Freundlich isotherm models, and were also well-explained by the Lagergren pseudo-second-order kinetic model. The maximum SO adsorption capacity of MRSB was found to be 41.59 mg/g, while for RSB the figure was 31.06 mg/g. The intra-particle diffusion model indicated that the intra-particle diffusion may not be the only rate-limiting step. The collective physical and chemical forces account for the adsorption mechanism of SO molecules by both RSB and MRSB adsorbents. The obtained results demonstrated that the magnetic biochar can partially enhance the SO adsorption capacity of its precursor biochar and also be easily separated from the solution by using an external magnet.

Rhodamine-B dye removal using aliquat-336 modified amberlite XAD-4 resin in fixed-bed columns in series

The present work reports studies on the effective removal of Rhodamine-B (RhB) using Aliquat-336 modified Amberlite XAD-4 resin in the fixed-bed columns in series. The effect of flow rate (Q = 2 to 6 mL·min^-1), bed height (h = 3.5 to 7 cm) and initial RhB dye concentration (C_in = 10 to 20 mg·L^-1) was studied. When a single column was used, 93% RhB dye was removed in 3 h at Q = 2 mL·min^-1, C_in = 10 mg·L^-1, and h = 7 cm. When three columns in series were used, almost 100% dye was removed until 80 h. The maximum breakthrough time (142 h) and saturation time (244 h) were found by keeping Q = 2 mL·min^-1, h = 7 cm of each column and C_in = 10 mg·L^-1. Mathematical modeling of the breakthrough curves was done by using Yoon-Nelson, Clark, Wolborska, and pore diffusion models. The Clark model best fitted the experimental data. The possible interaction mechanism between Aliquat-336 and RhB dye was proposed. The column was regenerated in continuous mode using 1 M HCl solution and maintaining a flow rate of 2 mL·min^-1.

Potential Application of Alternative Materials for Organic Pollutant Removal

The work aims to synthesize and characterize vegetal charcoal (or biochar) from Syzygium cumini (AC-SC), evaluating the adsorption capacity for dexamethasone drug (DEX) removal, using the kinetic and equilibrium adsorption. The samples were characterized by N₂ porosimetry, X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, zeta potential, and zero charge point. Adsorption equilibrium was carried out applying the Langmuir, Freundlich, Redlich-Peterson, Sips, and Toth models, and kinetic adsorption applied the pseudo-first order, pseudo-second order, Elovich, Avrami, and Weber-Morris models. AC-SC showed a heterogeneous and porous surface, negatively charged, crystalline structure, specific surface area of the 2.14 m² g^-1 and pH_ZCP = 7.36. About the effect of the AC-SC concentration, 5.0 g L^-1 showed the best DEX removal (53.02%), about the others' concentration (2.0 and 7.5 g L^-1). About the equilibrium and kinetic adsorption, the Sips model and pseudo-second order showed the best experimental data adjusted, indicating that the adsorption monolayer was dependent on the ions onto the biosorbent, with a maximum adsorption capacity of 0.744 mg g^-1 after 180 min. Therefore, AC-SC can be used as an alternative material in the removal of organic pollutants, such as drug removal.

Green Hydrogel-Biochar Composite for Enhanced Adsorption of Uranium

Uranium is the backbone of the nuclear fuel used for energy production but is still a hazardous environmental contaminant; thus, its removal and recovery are important for energy security and environmental protection. So far, the development of biocompatible, efficient, economical, and reusable adsorbents for uranium is still a challenge. In this work, a new orange peel biochar-based hydrogel composite was prepared by graft polymerization using guar gum and acrylamide. The composite's structural, morphological, and thermal characteristics were investigated via Fourier transform infrared (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. The composite's water absorption properties were investigated in different media. The performance of the prepared composite in adsorbing uranium (VI) ions from aqueous media was systematically investigated under varying conditions including solution's acidity and temperature, composite dose, contact time, and starting amount of uranium. The adsorption efficiency increased with solution pH from 2 to 5.5 and composite dose from 15 to 50 mg. The adsorption kinetics, isotherms, and thermodynamics parameters were analyzed to get insights into the process's feasibility and viability. The equilibrium data were better described through a pseudo-second-order mechanism and a Langmuir isotherm model, indicating a homogeneous composite surface with the maximum uranium (VI) adsorption capacity of 263.2 mg/g. The calculated thermodynamic parameters suggested that a spontaneous and endothermic process prevailed. Interference studies showed high selectivity toward uranium (VI) against other competing cations. Desorption and recyclability studies indicated the good recycling performance of the prepared composite. The adsorption mechanism was discussed in view of the kinetics and thermodynamics data. Based on the results, the prepared hydrogel composite can be applied as a promising, cost-effective, eco-friendly, and efficient material for uranium (VI) decontamination.

Sustainable remediation of hazardous environmental pollutants using biochar-based nanohybrid materials

Biochar is a well-known carbon material with diversified functionalities and excellent physicochemical characteristics with high wastewater treatment potential. This review aims to summarize recent advancements in the development of biochar and biochar-based nanohybrid materials as a potential tool for the removal of harmful organic compounds such as synthetic dyes/effluents. The formation of biochar using pyrolysis of renewable feedstocks and their applications in various industries are explained hereafter. The characteristics and construction of biochar-based hybrid materials are explained in detail. Diversity of feedstocks, including municipal wastes, industrial byproducts, agricultural, and forestry residues, endows different biochar types with a wide structural variety. The production of cost-effective biochar drives the interest in manipulating biochars and induces desire functionality using nanoscale reinforcements. Various types of biochars, such as magnetic biochar, layered nanomaterial coated biochar, nanometallic oxide composites, chemically and physically functionalized biochar, have been produced. With the aid of nanomaterial, hybrid biochar exhibits a high potential to remove toxic contaminants. Depending upon biochar type, dyes/effluents can be removed via different mechanisms, including the Fenton process, photocatalytic degradation, π-π interaction, electrostatic interaction, and physical adsorption. In conclusion, desired physicochemical features, and tunable surface properties of biochar present high potential material in removing organic dyes and other effluents. The blended biochar with different materials/nanomaterials endows broader development and multi-functional opportunities for treating dyes/effluents.

Potential Use of Biochar in Pit Latrines as a Faecal Sludge Management Strategy to Reduce Water Resource Contaminations: A Review

Faecal sludge management (FSM) in most developing countries is still insufficient. Sanitation challenges within the sub-Saharan region have led to recurring epidemics of water- and sanitation-related diseases. The use of pit latrines has been recognised as an option for on-site sanitation purposes. However, there is also concern that pit latrine leachates may cause harm to human and ecological health. Integrated approaches for improved access to water and sanitation through proper faecal sludge management are needed to address these issues. Biochar a carbon-rich adsorbent produced from any organic biomass when integrated with soil can potentially reduce contamination. The incorporation of biochar in FSM studies has numerous benefits in the control of prospective contaminants (i.e., heavy metals and inorganic and organic pollutants). This review paper evaluated the potential use of biochar in FSM. It was shown from the reviewed articles that biochar is a viable option for faecal sludge management because of its ability to bind contaminants. Challenges and possible sustainable ways to incorporate biochar in pit latrine sludge management were also illustrated. Biochar use as a low-cost adsorbent in wastewater contaminant mitigation can improve the quality of water resources. Biochar-amended sludge can also be repurposed as a useful economical by-product.

Malachite Green Removal by Activated Potassium Hydroxide Clove Leaf Agrowaste Biosorbent: Characterization, Kinetic, Isotherm, and Thermodynamic Studies

Although several approaches have been explored for the removal of dyes and other toxic materials from water as well as the entire environment, notwithstanding, researchers/scientists are still pursuing novel, low-cost, and eco-friendly biosorbents for the effective removal of such contaminants. Herein, clove leaves (CL) were utilized as a biosorbent for the sequestration of malachite green (MG) from a water-soluble solution. The CL was subsequently activated using potassium hydroxide (KOH) and characterized using the FTIR and FESEM to determine the functional groups on the activated clove leaves (CL-KOH) and the morphology of the adsorbent. The adsorption of MG was observed to be relatively dependent on the dosage of sorbent utilized, initial MG concentration, and sorption process contact time. The adsorption process of MG to CL was ideally described using the Dubinin–Radushkevich and Elovich models with the determination of maximum sorption capacity of approximately 131.6 mg·g-1. Furthermore, the thermodynamic parameters calculated showed that the adsorption of MG to the adsorbent was exothermic with the process involving physical sorption as well as chemical sorption processes with negligible adsorption energy. In conclusion, the study has revealed that the CL is a cost-effective biosorbent with high adsorption efficiency for the sequestration of MG from a water-soluble solution and can be recycled for further usage.

Castor Leaves-Based Biochar for Adsorption of Safranin from Textile Wastewater

The prospect of synthesizing biochar from agricultural wastes or by-products to utilize them as a promising adsorbent material is increasingly gaining attention. This research work focuses on synthesizing biochar from castor biomass (CBM) and evaluating its potential as an adsorbent material. Castor biomass-based biochar (CBCs) prepared by the slow pyrolysis process at different temperatures (CBC400 °C, CBC500 °C, and CBC600 °C for 1 h) was investigated for the adsorption of textile dye effluents (safranin). The pyrolysis temperature played a key role in enhancing the morphology, and the crystallinity of the biochar which are beneficial for the uptake of safranin. The CBC600 adsorbent showed a higher safranin dye removal (99.60%) and adsorption capacity (4.98 mg/g) than CBC500 (90.50% and 4.52 mg/g), CBC400 (83.90% and 4.20 mg/g), and castor biomass (CBM) (64.40% and 3.22 mg/g). Adsorption data fitted better to the Langmuir isotherm model than to the Freundlich isotherm model. The kinetics of the adsorption process was described well using the pseudo-second-order kinetic model. The study on the effect of the contact time for the adsorption process indicated that for CBC600, 80% dye removal occurred in the first 15 min of the contact time. After three regeneration cycles, CBC600 exhibited the highest dye removal efficiency (64.10%), highlighting the enhanced reusability of CBCs. The crystalline patterns, functional binding sites, and surface areas of the prepared CBCs (CBC400, CBC500, CBC600) were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller surface area measurements, respectively.

Physicochemical Interactions in Systems C.I. Direct Yellow 50—Weakly Basic Resins: Kinetic, Equilibrium, and Auxiliaries Addition Aspects

Intensive development of many industries, including textile, paper or plastic, which consume large amounts of water and generate huge amounts of wastewater-containing toxic dyes, contribute to pollution of the aquatic environment. Among many known methods of wastewater treatment, adsorption techniques are considered the most effective. In the present study, the weakly basic anion exchangers such as Amberlyst A21, Amberlyst A23 and Amberlyst A24 of the polystyrene, phenol-formaldehyde and polyacrylic matrices were used for C.I. Direct Yellow 50 removal from aqueous solutions. The equilibrium adsorption data were well fitted to the Langmuir adsorption isotherm. Kinetic studies were described by the pseudo-second order model. The pseudo-second order rate constants were in the range of 0.0609–0.0128 g/mg·min for Amberlyst A24, 0.0038–0.0015 g/mg·min for Amberlyst A21 and 1.1945–0.0032 g/mg·min for Amberlyst A23, and decreased with the increasing initial concentration of dye from 100–500 mg/L, respectively. There were observed auxiliaries (Na2CO3, Na2SO4, anionic and non-ionic surfactants) impact on the dye uptake. The polyacrylic resin Amberlyst A24 can be promising sorbent for C.I. Direct Yellow 50 removal as it is able to uptake 666.5 mg/g of the dye compared to the phenol-formaldehyde Amberlyst A23 which has a 284.3 mg/g capacity.