Adsorption performance and mechanism of iron-loaded biochar to methyl orange in the presence of Cr6+ from dye wastewater

An economical preparation strategy of magnetic biochar with high specific surface area for efficient removal of methyl orange

Magnetic biochar (MBC) was obtained from pepper straw by impregnation-microwave pyrolysis method. The pyrolysis temperature and FeCl3 impregnation concentration were investigated on the structural properties of MBC and the adsorption of methyl orange (MO) in water. Characterization results showed that pyrolysis temperature and iron species significantly increased the specific surface area of MBC, which could reach the maximum of 2038.61 m2/g, and also provided more active adsorption sites by promoting the generation of graphitized structures and surface polar functional groups. MBC0.2-900 was selected as the adsorbent for MO with the maximum adsorption capacity reached 437.18 mg·g-1, 3.4 times higher than the virgin biochar. The adsorption process was dominated by chemisorption as well as spontaneous and exothermic. The adsorption mechanisms included pore-filling interaction, π-π EDA interaction, electrostatic interaction, hydrogen bonding, and Lewis acid-base electron interaction. In addition, MBC also exhibited excellent separability and reusability as a low-cost adsorbent. This study provided some theoretical foundation and technological support for producing high-performance biochar and developing pollutant removal technology in wastewater.

Photocatalytic reduction of Cr(VI) using newly synthesized black phosphorus/ZnO nanocomposites

Removal of high toxic Cr(VI) with solar plays an important role in improving water pollution, but is facing a dilemma of developing excellent photocatalysts with high conversion efficiency and low cost. Different from traditional nano-structuring, this work focuses on the interfacial hybridization by considering the intrinsic difference in bonding interaction. Herein, we intentionally make some layered black phosphorus (BP) sheets with Van der Waals interaction to bond with ZnO surfaces, in which some additional electron channels can be formed by this multilevel atomic hybridization to accelerate carrier transfer and separation. Compared to the pristine ZnO and BP nanosheets, the light absorption and carrier separation efficiency can be sharply enhanced by this particular electronic structure, which makes the Cr reduction performance enhanced about 7.1 times. Our findings suggest a new insight into accelerating Cr(VI) reduction by designing interfacial atom hybridization.

Synergistic interactions and reaction mechanisms of biochar surface functionalities in antibiotics removal from industrial wastewater

Biochar, a carbon-rich material with a unique surface chemistry (high abundance of surface functional groups, large surface area, and well-distributed), has shown great potential as a sustainable solution for industrial wastewater treatment as compared to conventional industrial wastewater treatment techniques demand substantial energy consumption and generate detrimental byproducts. This critical review emphasizes the surface functionalities formation and development in biochar to enhance its physiochemical properties, for utilization in antibiotics removal. Factors affecting the formation of functionalities, including carbonization processes, feedstock materials, operating parameters, and the influence of pre-post treatments, are thoroughly highlighted to understand the crucial role of factors influencing biochar properties for optimal antibiotics removal. Furthermore, the research explores the removal mechanisms and interactions of biochar-based surface functionalities, hydrogen bonding, encompassing electrostatic interactions, hydrophobic interactions, π-π interactions, and electron donor and acceptor interactions, to provide insights into the adsorption/removal behavior of antibiotics on biochar surfaces. The review also explains the mechanism of factors influencing the removal of antibiotics in industrial wastewater treatment, including particle size and pore structure, nature and types of surface functional groups, pH and surface charge, temperature, surface modification strategies, hydrophobicity/hydrophilicity, biochar dose, pollutant concentration, contact time, and the presence of coexisting ions and other substances. Finally, the study offers reusability and regeneration, challenges and future perspectives on the development of biochar-based adsorbents and their applications in addressing antibiotics. It concludes by summarizing the key findings and emphasizing the significance of biochar as a sustainable and effective solution for mitigating antibiotics contamination in industrial wastewater.

Energetic utilization of corn stalk and elimination of methyl orange in ECMO-like integrated reactor: Co-occurrence of anaerobic digestion and aerobic treatment

For the simultaneous energetic utilization of corn stalk and azo-dye contaminated wastewater, an ECMO-like integrated reactor was come up to achieve the biogas production and azo-dye degradation during anaerobic digestion (AD). Methyl orange (MO) was selected as the model compound for azo-dye. The ECMO-like reactor included AD main reactor with a spray device and solid-liquid separation components, integrated with an aeration reactor for biogas slurry. Methane yields of corn stalks (100.82 mL/g VS) were highest in the ECMO-like reactor, compared with reactors without aeration. As a stable metabolite, 4-aminobenzenesulfonic acid (4-ABA) was detected in AD, while it was assumed that the metabolites can be further transformed in the ECMO-like reactor (R3), due to the 4-ABA removal efficiency as 92.87 % after 35 days' digestion. Class Alphaproteobacteria and Clostridia were assumed as functional microbes responding to aeration. Overall, this ECMO-like integrated reactor provided a novel biotechnology strategy for agricultural and azo dye waste treatment.

Enhanced Adsorption of Methyl Orange from Aqueous Phase Using Chitosan-Palmer Amaranth Biochar Composite Microspheres

To develop valuable applications for the invasive weed Palmer amaranth, we utilized it as a novel biochar source and explored its potential for methyl orange adsorption through the synthesis of chitosan-encapsulated Palmer amaranth biochar composite microspheres. Firstly, the prepared microspheres were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy and were demonstrated to have a surface area of 19.6 m2/g, a total pore volume of 0.0664 cm3/g and an average pore diameter of 10.6 nm. Then, the influences of pH, dosage and salt type and concentration on the adsorption efficiency were systematically investigated alongside the adsorption kinetics, isotherms, and thermodynamics. The results reveal that the highest adsorption capacity of methyl orange was obtained at pH 4.0. The adsorption process was well fitted by a pseudo-second-order kinetic model and the Langmuir isotherm model, and was spontaneous and endothermic. Through the Langmuir model, the maximal adsorption capacities of methyl orange were calculated as 495.0, 537.1 and 554.3 mg/g at 25.0, 35.0 and 45.0 °C, respectively. Subsequently, the adsorption mechanisms were elucidated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy investigations. It is indicated that electrostatic interactions, hydrogen bonding, π-π interactions and hydrophobic interactions between methyl orange and the composite microspheres were pivotal for the adsorption process. Finally, the regeneration studies demonstrated that after five adsorption-desorption cycles, the microspheres still maintained 93.6% of their initial adsorption capacity for methyl orange. This work not only presents a promising method for mitigating methyl orange pollution but also offers a sustainable approach to managing Palmer amaranth invasion.

Advancing the development of nanocomposite adsorbent through zinc-doped nickel ferrite-pinecone biochar for removal of chromium (VI) from wastewater

Leather and textile industrial effluents are the main disseminating routes for chromium contamination of water bodies, causing adverse impacts on public and environmental health. The attempt to remediate chromium through conventional wastewater treatment methods is inefficient. Therefore, this study aims to synthesize zinc-doped nickel ferrite pinecone biochar (Zn-NiF@PBC) nanocomposite for the removal of chromium from wastewater systems. The Zn-NiF@PBC nanocomposite was synthesized via the co-precipitation method. The properties of zinc-doped nickel ferrite (Zn-NiF) were effectively modified by blending with biochar at 1, 5, 10, and 15 % (w/w) which was successfully embedded with Zn-Ni ferrite nanoparticles. This was characterized and confirmed by typical adsorbent properties such as a high surface area of 104 m2/g, conducive pore volume of 0.117 cm3/g and pore size of 3.41 nm (BET), interactive multi-functional groups (FTIR), surface charge determination (pHpzc,), crystalline structure (XRD) and very rough surface morphology (SEM). The maximum chromium adsorption was found to be 95 % at the specific experimental condition of pH 3, adsorbent dose 1 g/50 mL, contact time 120 min, and initial chromium concentration 100 mg/L. The adsorption experimental data was best fitted with the Langmuir isotherm at R2 0.98 indicating the adsorption process was homogeneous and monolayer whereas the kinetics adsorption was resembling the second-order kinetic at R2 0.99. Moreover, the adsorption thermodynamics was spontaneous, endothermic, and increased the change in entropy. Finally, the regeneration of Zn-NiF@PBC was found to be effective up to five 5 cycles but gradually degrading in terms of removal efficiency after 3 cycles. In general, Zn-NiF@PBC can remediate chromium from wastewater with huge potential for scale-up and extend to other pollutants clear-up.

Application of carbon-based adsorbents in the remediation of micro- and nanoplastics

Micro-nano plastics (MNPs) are emerging contaminants that can easily enter the food chain, posing risks to both the aquatic ecosystem and human health. Various physical, biological, and chemical methods have been explored to remove MNPs from water, and recently, adsorption technology has gained attention as an effective approach. Among the potential candidates, carbon-based adsorbent has emerged as a promising choice due to their low cost, eco-friendly nature, and sustainability. This paper summarizes recent advancements in MNP removal using carbon-based adsorbents, with a focus on the modification methods and adsorption mechanisms. Additionally, the factors influencing the adsorption performance and the methods for characterizing the adsorption mechanism are analyzed. Finally, the advantages and disadvantages of carbon-based adsorbents over other adsorbents are discussed, along with the current state of sustainable recycling and future research prospects.

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).

Combined disposal of methyl orange and corn straw via stepwise adsorption-biomethanation-composting

Agriculture wastes have been proved to be the potential adsorbents to remove azo dye from textile wastewater, but the post-treatment of azo dye loaded agriculture waste is generally ignored. A three-step strategy including sequential adsorption-biomethanation-composting was developed to realize the co-processing of azo dye and corn straw (CS). Results showed that CS represented a potential adsorbent to remove methyl orange (MO) from textile wastewater, with the maximum MO adsorption capacity of 10.00 ± 0.46 mg/g, deriving from the Langmuir model. During the biomethanation, CS could serve as electron donor for MO decolorization and substrate for biogas production simultaneously. Though the cumulative methane yield of CS loaded with MO was 11.7 ± 2.28% lower than that of blank CS, almost complete de-colorization of MO could be achieved within 72 h. Composting could achieve the further degradation of aromatic amines (intermediates during the degradation of MO) and decomposition of digestate. After 5 days' composting, 4-aminobenzenesulfonic acid (4-ABA) was not detectable. The germination index (GI) also indicated that the toxicity of aromatic amine was eliminated. The overall utilization strategy gives novel light on the management of agriculture waste and textile wastewater.

Target-prepared sludge biochar-derived synergistic Mn and N/O induces high-performance periodate activation for reactive iodine radicals generation towards ofloxacin degradation

Converting waste activated sludge into catalysts for the removal of antibiotics in water fulfils the dual purpose of waste-to-resource and hazardous pollution elimination. In this study, sludge-derived biochar (SDB) for efficient periodate (PI) activation was first prepared via one-step pyrolysis of potassium permanganate-polyhexamethylenebiguanide conditioned sludge without additional modification. The SDB (750 °C)-PI system degraded 100% ofloxacin (OFL, 41.5 μM) within 6 min and was almost undisturbed by inorganic ions or humic acids. The experimental results confirmed that the predominant role of reactive iodine species (RIS) and the auxiliary involvement of singlet oxygen (1O2) jointly contributed to the OFL degradation. Theoretical calculations further indicated that the synergy between Mn and N/O induced local charge redistribution and improved electron transfer capability of SDB, leading to the formation of electron-rich Mn sites and enhanced Mn(II)↔Mn(III)↔Mn(IV) redox to promote PI activation. More importantly, the enhanced adsorption and charge transfer of PI on the Mn site of the Mn-N/O-C structures induced the I-O bond stretching and the rapid generation of RIS. This study offered a cost-effective strategy for developing SDB-based catalysts, further advancing the comprehension of sludge management and the intricate mechanisms underlying RIS formation in PI-advanced oxidation processes.

Effective removal of malachite green from local dyeing wastewater using zinc-tungstate based materials

The frequent use of an industrial dye such as malachite green (MG) has caused major water body deterioration and is one of the most pressing global challenges, demanding effective treatment techniques. To solve these issues, a simplistic method was developed to synthesize zinc-tungstate (ZnWO4) nanoparticles and also dope the surface matrix of the ZnWO4 nanoparticles using nonmetals of boron (B), carbon (C), and nitrogen (N) at different ratios for enhanced MG removal from wastewater. The prepared nanomaterials were characterized by different methods for crystal structure composition, surface properties, surface morphology, microstructures, functional groups, and elemental oxidation states. The BET analysis revealed a mesoporous structure with surface areas of 30.740 m2/g for ZnWO4, 38.513 m2/g for ZnWO4@BCN, 37.368 m2/g for ZnWO4@BCN/B, 39.325 m2/g for ZnWO4@BCN/C, and 45.436 m2/g for ZnWO4@BCN/N nanocomposites. The best removal of MG was accomplished at pH (8), contact period (50 min), nanoadsorbent dose (0.8 g/L), initial MG concentration (20 mg/L), and temperature (303 K). The maximum adsorption capacities of ZnWO4 and ZnWO4@BCN/N towards MG were 218.645 and 251.758 mg/g, respectively. At equilibrium, the Freundlich isotherm and pseudo-second-order kinetic models were the best fits for the experimental data of MG adsorption on both nanoadsorbents. After eight cycles of adsorption and desorption, both ZnWO4 and ZnWO4@BCN/N were found to be good at removing MG, with efficiencies of 71.00 and 74.20%, respectively. Thermodynamic investigations further validated the spontaneity and endothermic nature of the adsorption process. All study findings confirm the nanoadsorbents exceptional capability and economic feasibility for removing MG dye.

Optimizing adsorption performance of sludge-derived biochar via inherent moisture-regulated physicochemical properties

Understanding the impact of abundant inherent moisture in sewage sludge on the physicochemical properties and adsorption applications of sludge-derived biochar (SDB) contributed significantly to promoting economical sludge reuse. The moisture (0-80%) contributed to the development of micropore and mesopore in SDB at 400 °C, resulting in a maximum increase in specific surface area (SSA) and total pore volume (TPV) of SDB by 38.47% (84.811-117.437 m2/g) and 92.60% (0.0905-0.1743 m3/g), respectively. At 600/800 °C, moisture only facilitated mesopore formation, while was exacerbated with increasing moisture content. Despite reduction in SSA during this stage, TPV increased by a maximum of 20.47% (0.1700-0.2048 m3/g). The presence of moisture during pyrolysis led to an increase in the formation of 3-5 thickened benzene rings and defective structures in SDB, along with more C=O, O-C=O/-OH, pyrrole N, pyridine N, and thiophene. As a result, moisture (40%/80%) increased the maximum adsorption capacity (76.2694-88.0448/90.1190 mg/g) of SDB (600 °C) for tetracycline, mainly due to enhanced pore filling effect and hydrogen bonding induced by improved physicochemical properties. This study offered a novel approach for optimizing the performance of SDB adsorption applications by manipulating the sludge moisture, which is critical for practical sludge management.

Simultaneous adsorption of ciprofloxacin and Cu2+ using Fe and N co-doped biochar: Competition and selective separation

The treatment of combined antibiotics and heavy metals pollution is a critical challenge. Herein, iron and nitrogen co-doped biochar (Fe/N-BC) was synthesized using rape straw as precursor, and applied for the adsorption of ciprofloxacin (CIP) and Cu2+ in single and binary systems. The qmax for CIP and Cu2+ were 46.45 mg g-1 and 30.77 mg g-1, respectively. Adsorption decreased in a binary matrix, indicating that there was a competitive effect between CIP and Cu2+, which might be due to CIP and Cu2+ sharing similar active adsorption sites on Fe/N-BC. Interestingly, CIP and Cu2+ co-adsorption was a pH-dependent process. Fe/N-BC has potential to highly selectively separate CIP/Cu2+ from mixed solutions through adjusting pH values. Furthermore, adsorption mechanisms were systematically investigated in this research. This research could help to provide a deeper understanding of the synchronously removing specific antibiotics and heavy metals by biochar adsorbents.

A highly efficient and sustainable photoabsorber in solar-driven seawater desalination and wastewater purification

Producing freshwater from seawater and wastewater is of great importance through interfacial solar steam generation (ISSG). Herein, the three-dimensional (3D) carbonized pine cone, CPC1, was fabricated via a one-step carbonization process as a low-cost, robust, efficient, and scalable photoabsorber for the ISSG of seawater as well as a sorbent/photocatalyst for use in wastewater purification. Taking advantage of the large solar-light-harvesting ability of CPC1 due to the presence of carbon black layers on the 3D structure, its inherent porosity, rapid water transportation, large water/air interface, and low thermal conductivity, a conversion efficiency of 99.8% and evaporation flux of 1.65 kg m-2 h-1 under 1 sun (kW m-2) illumination were achieved. After carbonization of the pine cone, its surface becomes black and rough, which leads to an increase in its light absorption in the UV-Vis-NIR region. The photothermal conversion efficiency and evaporation flux of CPC1 did not change significantly during 10 evaporation-condensation cycles. CPC1 exhibited good stability under corrosive conditions without significant change in its evaporation flux. More importantly, CPC1 can be used to purify seawater or wastewater by the removal of organic dyes as well as by the reduction of polluting ions, like nitrate ions in sewage.

Simultaneously Cationic and Anionic Dyes Elimination via Magnetic Hydrochar Prepared from Copper Slag and Pinewood Sawdust

In practical wastewater, cationic and anionic dyes usually coexist, while synergistic removal of these pollutants is difficult due to their relatively opposite properties. In this work, copper slag (CS) modified hydrochar (CSHC) was designed as functional material by the one-pot method. Based on characterizations, the Fe species in CS can be converted to zero-valent iron and loaded onto a hydrochar substrate. The CSHC exhibited efficient removal rates for both cationic dyes (methylene blue, MB) and anionic dyes (methyl orange, MO), with a maximum capacity of 278.21 and 357.02 mg·g^-1, respectively, which was significantly higher than that of unmodified ones. The surface interactions of MB and MO between CSHC were mimicked by the Langmuir model and the pseudo-second-order model. In addition, the magnetic properties of CSHC were also observed, and the good magnetic properties enabled the adsorbent to be quickly separated from the solution with the help of magnets. The adsorption mechanisms include pore filling, complexation, precipitation, and electrostatic attraction. Moreover, the recycling experiments demonstrated the potential regenerative performance of CSHC. All these results shed light on the co-removal of cationic and anionic contaminates via these industrial by-products derived from environmental remediation materials.

Effective removal of tetracycline antibiotics from water by magnetic functionalized biochar derived from rice waste

The effective removal of tetracycline antibiotics (TCs) from water is of great significance and remains a big challenge. In this work, a novel magnetized biochar (magnetic functionalized carbon microsphere, MF-CMS) was prepared by the coupling hydrothermal carbonization and pyrolysis activation of starch-rich rice waste using ZnCl₂ and FeCl₃ as activators. As the MF-CMS dose was 2.0 g/L, the initial concentration of TCs was 100 mg/L, the removal rates of tetracycline, doxycycline, oxytetracycline, and chlortetracycline were 96.02%, 96.10%, 96.52%, and 85.88%, respectively. The best modeled on pseudo second order, Langmuir adsorption model, and intraparticle diffusion kinetic models suggested that both chemisorption and physisorption occurred in all removal processes, in which chemisorption dominated. TCs were efficiently adsorbed through the combined effects of pore filling, electrostatic attraction, π-π interactions, and complexation reactions of surface functional groups (such as γ-Fe₂O₃ and FeOOH). The removal rates of TCs after five cycles approximately decreased by 20%. And the cycling and metal ion release experiments of MF-CMS indicated that MF-CMS had good reusability, stability, and safety. The estimated cost of preparing MF-CMS is 5.91 USD per kg, and 1 kg of MF-CMS (consuming 8 kg of waste rice) can approximately treat 0.55 tons of TCs wastewater. Overall, the magnetic biochar derived from starch-rich rice waste as an adsorbent has promising and effective for the removal of TCs from water, but also provides a new idea for the resourceful treatment of solid waste.

Synergistic adsorption and oxidation of trivalent antimony from groundwater using biochar supported magnesium ferrite: Performances and mechanisms

Antimony (Sb) pollution is considered an environmental problem, since Sb is toxic and carcinogenic to humans. Here, a novel biochar supported magnesium ferrite (BC@MF) was adopted for Sb(III) removal from groundwater. The maximum adsorption capacity was 77.44 mg g^-1. Together with characterization, batch experiments, kinetics, isotherms, and thermodynamic analyses suggested that inner-sphere complexation, H-bonding, and electrostatic interactions were the primary mechanisms. C-C/CC, C-O, and O-CO groups and Fe/Mg oxides might have acted as adsorption sites. The adsorbed Sb(III) was oxidized to Sb(V). The generation of reactive oxygen species, iron redox reaction, and oxidizing functional groups all contributed to Sb(III) oxidation. Furthermore, the fixed-bed column system demonstrated a satisfactory Sb removal performance; BC@MF could treat ∼6060 BV of simulated Sb-polluted groundwater. This research provides a promising approach to sufficiently remove Sb(III) from contaminated groundwater, providing new insights for the development of innovative strategies for heavy metal removal.

Treatment of industrial ferric sludge through a facile acid-assisted hydrothermal reaction: Focusing on dry mass reduction and hydrochar recyclability performance

Large amounts of Fenton sludge and waste activated sludge (WAS) are mixed as ferric sludge (FS) in most industrial wastewater treatment plants. The treatment of such waste represents a challenge and quantity-dependent cost, so that a reliable way for FS waste reduction is required. In this study, we develop a facile acid-assisted hydrothermal treatment (HT) for the cost-efficient treatment of hazardous FS waste. Sulfuric acid was dosed at 0.25 mL/g dry solid (DS) to the HT process, which significantly increased the total solid mass reduction (TMR) by 25.1 % and dry mass reduction (DMR) by 104.4 %. The participation of sulfuric acid during the HT process changed the HT reaction pathway from dehydration to demethylation based on the analysis of the derivative thermogravimetric and Van Krevelen diagram. The addition of sulfuric acid improved the release of Fe from FS by 52.9 %, which contributed to the DMR. During the acid-assisted HT, Fe(III) was effectively reduced to Fe(II) within the produced hydrochar, which can be recycled for the Fenton reaction during the degradation of actual industrial wastewater such as pharmaceutical wastewater. Moreover, Sulfuric acid facilitated the generation of sulfonated hydrochar, which was efficient as an adsorbent for the complete removal of some metals such as Cu(II) - cation metal (98.8 %) and Cr(VI) - anion metal (99.9 %). This study firstly provides a novel and reliable approach for hazardous FS reduction and pointed out the recycling of hydrochar as the supplement for the Fenton reaction and adsorbents for some hazardous heavy metals.

Wastewater treatment: A universal, scalable and recyclable catalyst with adjustable activity for diverse dyes degradation

The growing concern over water shortage and pollution is propelling and accelerating the development of sewage treatment technologies. Among them, the catalytic hydrogenation method is highly recommended from a sustainable perspective, because it can turn toxic pollutants into valuable raw materials. The catalyst with excellent activity and stability plays a critical role in this "trash to treasure" approach. Herein, we proposed a novel economical, scalable and recyclable candidate catalyst, i.e., the copper nanoparticles supported on zinc oxide nanowire array (Cu-ZnO NWA), for realizing efficient and stable dye wastewater treatment. The salix argyracea-shaped Cu-ZnO NWA displays very outstanding universality and controllability towards the catalytic hydrogenation reactions of diverse dyes, owing to the fact that ZnO nanowire array not only offers a platform to realize stable and homogeneous dispersion of Cu nanoparticles, but also provides a large quantity of catalytically active sites. More attractively, its synthetic method can be facilely extended to various conductive substrates through combined electrodeposition and hydrothermal technique, showing its general applicability for the surface assembly of sewage treatment facilities. Benefiting from above advantages, this proposal offers an attractive approach for large-scale and continuous decolorization of dye wastewater, and presents a broad application prospect in the textile printing industry.

Recyclable Magnetic Iron Immobilized onto Chitosan with Bridging Cu Ion for the Enhanced Adsorption of Methyl Orange

Chitosan (CS) is a natural and low-cost adsorbent for capturing metal ions and organic compounds. However, the high solubility of CS in acidic solution would make it difficult to recycle the adsorbent from the liquid phase. In this study, the CS/Fe₃O₄ was prepared via Fe₃O₄ nanoparticles immobilized onto a CS surface, and the DCS/Fe₃O₄-Cu was further fabricated after surface modification and the adsorption of Cu ions. The meticulously tailored material displayed the sub-micron size of an agglomerated structure with numerous magnetic Fe₃O₄ nanoparticles. During the adsorption of methyl orange (MO), the DCS/Fe₃O₄-Cu delivered a superior removal efficiency of 96.4% at 40 min, which is more than twice the removal efficiency of 38.7% for pristine CS/Fe₃O₄. At an initial MO concentration of 100 mg L^-1, the DCS/Fe₃O₄-Cu exhibited the maximum adsorption capacity of 144.60 mg g^-1. The experimental data were well explained by the pseudo-second-order model and Langmuir isotherm, suggesting the dominant monolayer adsorption. The composite adsorbent still maintained a large removal rate of 93.5% after five regeneration cycles. This work develops an effective strategy to simultaneously achieve high adsorption performance and convenient recyclability for wastewater treatment.

Adsorptive removal of hazardous dye (crystal violet) using bay leaves (Laurus nobilis L.): surface characterization, batch adsorption studies, and statistical analysis

In this study, the surface properties of Laurus nobilis L. were determined by inverse gas chromatography. From this, the surface of Laurus nobilis L. was found to be an acidic ([Formula: see text]). Then, the adsorption of hazardous crystal violet dye on Laurus nobilis L. was examined. For the adsorption process, the optimum conditions were determined as contact time (60 min), adsorbent dosage (1.0 g/L), agitation rate (200 rpm), and initial pH (≅ 7). The efficiencies of initial concentration, contact time, temperature, and their binary combinations on the improvement of adsorption percentage were statistically investigated via three different two-way ANOVA analyses. Adsorption data were applied to different isotherms, and it was determined that the Langmuir isotherm (r² = 0.9998) was the most suitable isotherm for the adsorption process. The [Formula: see text] value was calculated as 400.0 mg/g at 25 °C from the Langmuir isotherm. According to kinetic models, it was observed that the adsorption occurred in three steps. According to enthalpy (+ 7.52 kJ/mol), activation energy (+ 8.91 kJ/mol), and Gibbs free energy (- 30.0 kJ/mol) values, it was determined that the adsorption occurred endothermically and spontaneously. As a result of reusability studies, it was determined that the adsorbent could be used repeatedly.

Removal of Cr(VI) from aqueous solution by a novel ZnO-sludge biochar composite

The incorporation of ZnO into biochar has become a promising way to obtain adsorbents with enhanced adsorption capacity. In this study, a low-cost ZnO-sludge biochar composite (ZBC) was prepared by a simply in situ method using sewage sludge biochar (SBC) and zinc acetate, as well as employed for Cr(VI) adsorption in water. The results of XPS and FT-IR suggested that the ZBC surface had more functional groups such as -COOH, -OH, -C-O, ZnO, etc. Compared with SBC, the BET-specific surface area of the ZBC increased from 8.82 to 41.24 m²·g^-1, which provides potential advantages for Cr(VI) uptake. Benefiting from ZnO incorporation, about an 18% increase in Cr(VI) removal efficiency was obtained. The maximum removal efficiency and equilibrium adsorption amount of ZBC for Cr(VI) reached 98.4% and 33.87 mg·g^-1, respectively. The adsorption was spontaneous and endothermic nature, and coincided nicely with pseudo-second-order kinetics and Langmuir isotherm. The analyses indicated that Cr(VI) removal by ZBC was predominantly via electrostatic attraction, surface complexation, ion exchange, and reduction. This study provided valuable insights into the problem of sludge disposal and provided a new and effective method for Cr(VI) removal.

A sustainable reuse strategy of converting waste activated sludge into biochar for contaminants removal from water: Modifications, applications and perspectives

Conversion of sewage sludge to biochar for contaminants removal from water achieves the dual purpose of solid waste reuse and pollution elimination, in line with the concept of circular economy and carbon neutrality. However, the current understanding of sludge-derived biochar (SDB) for wastewater treatment is still limited, with a lack of summary regarding the effect of modification on the mechanism of SDB adsorption/catalytic removal aqueous contaminants. To advance knowledge in this aspect, this paper systematically reviews the recent studies on the use of (modified) SDB as adsorbents and in persulfate-based advanced oxidation processes (PS-AOPs) as catalysts for the contaminants removal from water over the past five years. Unmodified SDB not only exhibits stronger cation exchange and surface precipitation for heavy metals due to its nitrogen/mineral-rich properties, but also can provide abundant catalytic active sites for PS. An emphatic summary of how certain adsorption removal mechanisms of SDB or its catalytic performance in PS-AOPs can be enhanced by targeted regulation/modification such as increasing the specific surface area, functional groups, graphitization degree, N-doping or transition metal loading is presented. The interference of inorganic ions/natural organic matter is one of the unavoidable challenges that SDB is used for adsorption/catalytic removal of contaminants in real wastewater. Finally, this paper presents the future perspectives of SDB in the field of wastewater treatment. This review can contribute forefront knowledge and new ideas for advancing sludge treatment toward sustainable green circular economy.

Applications of functionalized magnetic biochar in environmental remediation: A review

Magnetic biochar (MBC) is extensively applied on contaminants removal from environmental medium for achieving environmental-friendly remediation with reduction of secondary pollution owing to its easy recovery and separation. However, the summary of MBC synthesis methods is still lack of relevant information. Moreover, the adsorption performance for pollutants by MBC is limited, and thus it is imperative to adopt modification techniques to enhance the removal ability of MBC. Unfortunately, there are few reviews to present modification methods of MBC with applications for removing hazardous contaminants. Herein, we critically reviewed (i) MBC synthetic methods with corresponding advantages and limitations; (ii) adsorption mechanisms of MBC for heavy metals and organic pollutants; (iii) various modification methods for MBC such as functional groups grafting, nanoparticles loading and element doping; (iv) applications of modified MBC for hazardous contaminants adsorption with deep insight to relevant removal mechanisms; and (v) key influencing conditions like solution pH, temperature and interfering ions toward contaminants removal. Finally, some constructive suggestions were put forward for the practical applications of MBC in the near future. This review provided a comprehensive understanding of using functionalized MBC as effective adsorbent with low-cost and high-performance characteristics for contaminated environment remediation.

Biochar-based compost: a bibliometric and visualization analysis

The co-application of biochar compost as organic amendment for crop production and soil remediation has gained momentum due to their positive effect on plant growth and soil quality improvement. The application of biochar and compost which are green and cost-effective soil remediators would promote the availability and distribution of food, planetary conservation, alleviate poverty, and enhance the attainment of Sustainable Millennium Development Goals (SDGs). A bibliometric analysis was conducted to overview research on biochar compost from 2011 to 2021. Two hundred and fifty-four research papers were retrieved from the Scopus database and analyzed using VOS viewer. Analysis revealed that 217 (85.43%) were articles, 21 (8.27%) were conference papers, and 12 (4.72%) were review papers. The results showed an exponential increase in the number of publications. The most productive countries in the investigated subject were China (49), followed by USA (36), Australia (29), Italy (28), Germany (25), and Indonesia (20). After the search terms, 'soil,' which had links with keywords like 'soil fertility,' 'soil quality,' 'soil pollution,' 'phosphorus,' 'nitrogen,' 'maize,' 'greenhouse gas,' etc., had the highest occurrences (94). From the results of the current hotspot research in the field, the effect of biochar-compost mixture and co-composted biochar on soil remediation is currently being studied by several researchers. Biochar and compost incorporation in soil reduce the uptake of pollutants by plants which consequently increase essential nutrients for plant and soil productivity.

Biochars and activated carbons as adsorbents of inorganic and organic compounds from multicomponent systems - A review

Biochars are obtained by biomass pyrolysis, whereas activated carbon is a biochar that has undergone chemical or physical activation. Owing to the large surface area and easy surface modification both solids are widely applied as adsorbents. They are low-costs materials, they could be regenerated and their disposal is not troublesome. Adsorption of heavy metals, dyes, pharmaceuticals on the surface of biochars and activated carbons, from simple systems of adsorbate containing only one compound, are described extensively in the literature. The present paper provides an overview of reports on adsorption of inorganic and organic compounds onto these two types of adsorbents from the mixed adsorbate systems. The described adsorbate systems have been divided into those consisting of: two or more inorganic ions, two or more organic compounds and both of them (inorganic and organic ones). The research of this type is carried out much less frequently due to the more complicated description of interactions in the mixed adsorbate systems.

Adsorption of dyes methyl violet and malachite green from aqueous solution on multi-step modified rice husk powder in single and binary systems: Characterization, adsorption behavior and physical interpretations

A novel modified rice husk (MRH) has been prepared for removing cationic dyes in both single system and binary system. SEM-EDS, FT-IR, XRD and XPS were used to characterize the physical and chemical properties of MRH. It showed that the maximum adsorption capacity of MRH for methyl violet (MV) and malachite green (MG) in single system was 154.49 and 996.97 mg g^-1, while in binary system was 530.94 and 408.58 mg g^-1, respectively. The experimental results showed that the pseudo-second-order kinetic model was better to describe the kinetic behavior of MV and MG adsorption. By using double layer adsorption model, we found that the n_D for MV adsorption were 2.52, 2.65 and 3.34 at 298, 308 and 318 K, respectively, and the n_D for MG adsorption were 4.59, 4.85 and 4.30, respectively. These results illustrated that multiple dye molecules were adsorbed on one adsorption site in non-parallel direction, indicating that the adsorption of dyes is multi-molecular mechanism. Furthermore, synergistic and antagonistic adsorption might be existed simultaneously in binary system. In summary, MRH has been shown well adsorption properties and reusability and our finding might provide a new idea for developing low-cost, efficient and reusable adsorbent to remove dyes from wastewater.

Adsorptive removal of sulfosalicylic acid from aqueous medium by iron(III)-loaded magnetic chitosan/graphene oxide

In this study, an iron(III)-loaded magnetic chitosan/graphene oxide composite (Fe-MCG) was synthesized and applied for the adsorptive removal of sulfosalicylic acid (SSA) in aqueous solution. The results obtained from the application of various characterization techniques such as scanning electron microscopy (SEM), vibrating-sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS) prove the successful formation of the composite with enhanced microstructure and superparamagnetic properties. The adsorption capacity of Fe-MCG towards SSA via batch mode reaches up to 135 mg/g at 293 K. The adsorption of SSA onto Fe-MCG is driven by monolayer adsorption with the chemical and physical adsorption processes both playing active roles. The Langmuir isotherm and pseudo-second-order kinetic models were observed to best describe the equilibrium adsorption and kinetic processes, respectively. The values obtained for the associated thermodynamic parameters confirm that the adsorptive process is spontaneous, exothermic and entropy-increasing. The efficacy and reusability of the spent Fe-MCG was studied using 0.01 mol/L NaOH solution. The kinetic process for the desorption of SSA from Fe-MCG is well described by the pseudo-second-order kinetic model. Based on the experimental results and XPS analysis, the underlying mechanisms for the uptake of SSA onto Fe-MCG involve electrostatic forces, complexation, π-π stacking, and hydrogen bonding. Overall, the excellent features of Fe-MCG enhance its potential as an adsorbent for the sequestration of SSA in environmental media.

A novel biowaste-based biosorbent material for effective purification of methylene blue from water environment

The biowaste left over from the fixed oil biorefinery process of Nigella sativa L. plant was used as a new biosorbent for the biosorption of synthetic dye of methylene blue from water environment in this study. The main variables of biosorption operation such as methylene blue concentration, time, pH, and biosorbent amount were optimized by the batch-type experiments. The characterization, kinetics, equilibrium, and thermodynamics works were conducted to show the nature of methylene blue biosorption. The studies of Fourier transform infrared spectroscopy and Scanning electron microscopy indicated that the biosorbent possessed an inhomogeneous surface morphology including many cavities and protuberances, and a rich functional group profile. The optimum values of operating variables studied for the biosorption of methylene blue were determined as methylene blue concentration of 15 mg L^-1, time of 360 min, pH of 8, and biosorbent amount of 10 mg. The experimental data of methylene blue biosorption followed the kinetics and isotherm models of pseudo-second-order (R²: 0.98, AdjR²: 0.98, and RMSE: 8.97) and Dubinin-Radushkevich (R²: 0.99, AdjR²: 0.98, and RMSE: 6.84), respectively, based on the statistical tests of coefficient of determination (R²), adjusted coefficient of determination (AdjR²), and root mean squared error (RMSE). The biosorption of methylene blue was a physical, spontaneous, and energetically favorable process (E_DR: 3.48 kJ mol^-1 and ΔG°: (-14.51) - (-10.02) kJ mol^-1). This residual biological material from the fixed oil biorefinery process exhibited higher biosorption performance (187.46 mg g^-1) than own unrefined (virgin) form and its modified, activated, and composite forms and many other sorbents reported in the literature. Hereby, the current work showed that this novel biowaste-based material could be used as an environmentally and economically promising biosorbent to effectively purify methylene blue from aquatic environment.

RSM, ANN-GA and ANN-PSO modeling of SDBS removal from greywater in rural areas via Fe2O3-coated volcanic rocks

Decontamination and reuse of greywater in rural areas has attracted increasing attention. Typical contaminants in grey water are SDBS, which has a stubborn molecular structure. In this study, Fe₂O₃-coated volcanic rocks (Fe₂O₃-VR) prepared from FeCl₃ solution by a heating evaporation method can reach 95% removal of SDBS, which is 80% higher than before. The effect of contact time, pH, initial concentration, FeCl₃ solution concentration, adsorbent dosage and calcination temperature on the removal rate was researched and modeled by response methodology (RSM) and artificial neural network (ANN). Based on the univariate test, the Box-Behnken design method was used to establish the data sample, which represented a quadratic polynomial model with p-value <0.001, R² = 0.9872, while the ANN model has the better performance with R² = 0.9961. The weights of the BP-ANN model were further analyzed using the Garson equation, and the results showed that the validity ranking of the variables was as follows: contact time (37.31%) > calcination temperature (29.43%) > dosage (24.44%) > initial concentration (17.18%) > FeCl₃ solution concentration (17.18%) > pH (11.56%). Genetic algorithm (GA) and particle swarm optimization (PSO) were selected to optimize the process parameters. The results showed that ANN-PSO methodology presented a satisfactory alternative and the predicted removal efficiency was 99.9982% with relative error = 0.2230. The optimum level of contact time, pH, initial SDBS concentration, FeCl₃ solution concentration, adsorbent dosage and calcination temperature is 136.45 min, 5.64, 22.4 mg L⁻¹, 0.3 mol L⁻¹, 83.21 g L⁻¹, 274.02 °C, respectively. Moreover, Fe₂O₃-VR was characterized via instrumental analyses (SEM-EDS, FTIR, XRD, BET).

This paper provides a new method for SDBS removal and parameter optimization of the adsorption process using RSM and ANN models.

Efficient recovery of Cr(vi) from electroplating wastewater by iron-modified sludge-based hollow-structured porous carbon: coexistence effects and competition for adsorption

In the present work, porous carbon was made from sewage sludge and hybrid liriodendron leaves, and modified with iron ions (Fe@LS-BC) carried out on Cr(vi) in aqueous solution from a single-component system and in competitive biosorption with methyl orange (MO) from a binary-component system. The iron ion-modified porous carbon (Fe@LS-BC) showed higher efficiency in the removal of Cr(vi) compared to porous carbon prepared by the co-pyrolysis of sludge and hybrid liriodendron leaves. The incorporation of the Fe element improved the ability of the material to redox Cr(vi), while imparting magnetic characteristics to the porous carbon and improving the reusability of the porous carbon. On the other hand, Fe@LS-BC exhibited a better pore volume, facilitating the contact of the material with Cr(vi) ions. The highest adsorption capacity was 0.33 mmol g⁻¹, and the adsorption experimental results for the single-component and binary-component systems of Cr(vi) matched well with the Langmuir–Freundlich models. When the concentration of MO was 0.2 and 0.8 mmol L⁻¹, respectively, the highest adsorption capacity of Cr(vi) was 0.35 and 0.46 mmol g⁻¹ in the binary system. The positively charged N–CH₃⁺ on the MO molecule promoted the electrostatic adsorption between HCrO₄⁻, CrO₄²⁻, and Fe@LS-BC, and increased the adsorption potential of Cr(vi).

Mechanism for the adsorption of hexavalent chromium and methyl orange in a binary system.