Facile low-temperature one-step synthesis of pomelo peel biochar under air atmosphere and its adsorption behaviors for Ag(I) and Pb(II)

Fe Crystalline Phases in Fe/C Composites Modulated the Selective Adsorption of Pb(II) from Industrial Wastewater with Cd(II): An Electronic-Scale Perspective

Fe oxide or Fe0-based materials display weak removal capacity for Pb(II), especially in the presence of Cd(II), and the electronic-scale mechanisms are not reported. In this study, Fe3C(220) modified black carbon (BC) [Fe3C(220)@BC] with high adsorption and selectivity for Pb(II) from industrial wastewater with Cd(II) was developed. The quantitative experiment suggested that Fe species accounted for 80.5-100 and 18.4-33.8% of Pb(II) and Cd(II) removal, respectively. Based on X-ray absorption near-edge structure analysis, 57.3% of adsorbed Pb2+ was reduced to Pb0; however, 61.6% of Cd2+ existed on Fe3C@BC. Density functional theory simulation unraveled that Cd(II) adsorption was attributed to the cation-π interaction with BC, whereas that of Pb(II) was ascribed to the stronger interactions with different Fe phases following the order: Fe3C(220) > Fe0(110) > Fe3O4(311). Crystal orbital bond index and Hamilton population analyses were innovatively applied in the adsorption system and displayed a unique discovery: the stronger Pb(II) adsorption on Fe phases was mediated by a combination of covalent and ionic bonding, whereas ionic bonding was mainly accounted for Cd(II) adsorption. These findings open a new chapter in understanding the functions of different Fe phases in mediating the fate and transport of heavy metals in both natural and engineered systems.

Monitoring of copper adsorption on biochar using spectral induced polarization method

Copper contaminant generated from mining and industrial smelting poses potential risks to human health. Biochar, as a low-energy and cost-effective biomaterial, holds value in Cu remediation. Spectral Induced Polarization (SIP) technique is employed in this study to monitor the Cu remediation processes of by biochar in column experiments. Cation exchange at low Cu2+ concentrations and surface complexation at high Cu2+ concentrations are identified as the major mechanisms for copper retention on biochar. The normalized chargeability (mn) from SIP signals linearly decreased (R2 = 0.776) with copper retention under 60 mg/L Cu influent; while mn linearly increases (R2 = 0.907, 0.852) under high 300 and 700 mg/L Cu influents. The characteristic polarizing unit sizes (primarily the pores adsorbing Cu2+) calculated from Schwartz equation match well with experimental results by mercury intrusion porosimetry (MIP). It is revealed that Cu2+ was driven to small pores (∼3 μm) given high concentration gradient (influent Cu2+ concentration of 700 mg/L). Comparing to activated carbon, biochar is identified as an ideal adsorbent for Cu remediation, given its high adsorption capacity, cost-effectiveness, carbon-sink ability, and high sensitivity to SIP responses - the latter facilitates its performance assessment.

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.

Synthesis of metal-organic frameworks with multiple nitrogen groups for selective capturing Ag(I) from wastewater

As a noble metal with extremely high economic benefits, the recovery of silver ions has attracted a particular deal of attention. However, it is a challenge to recover silver ions efficiently and selectively from aqueous solutions. In this research, the novel metal-organic frameworks (MOFs) adsorbent (Zr-DPHT) is prepared for the highly efficient and selective recovery of silver ions from wastewater. Experimental findings reveal that Zr-DPHT's adsorption of Ag(I) constitutes an endothermic process, with an optimal pH of 5 and exhibits a maximum adsorption capacity of 268.3 mg·g-1. Isotherm studies show that the adsorption of Ag(I) by Zr-DPHT is mainly monolayer chemical adsorption. Kinetic studies indicate that the internal diffusion of Ag(I) in Zr-DPHT may be the rate-limiting step. The mechanism for Ag(I) adsorption on Zr-DPHT involves electrostatic interactions and chelation. In competitive adsorption, Ag(I) has the largest partition coefficient (9.64 mL·mg-1), indicating a strong interaction between Zr-DPHT and Ag(I). It is proven in the adsorption-desorption cycle experiments that Zr-DPHT has good regeneration performance. The research results indicate that Zr-DPHT can serve as a potential adsorbent for efficiently and selectively capturing Ag(I), providing a new direction for MOFs in the recycling field of precious metals.

Enhanced Adsorptive Removal of Tetracycline by Phosphomolybdic Acid-Modified Low-Temperature Sludge Biochar

Increasing the adsorption capacity and reducing the energy consumption of sludge biochar during preparation is important. In this study, a new modification method was developed to prepare phosphomolybdic acid-modified sludge biochar through the low-temperature pyrolysis of sewage sludge using phosphomolybdic acid as a modifier. Tetracycline was used to assess the adsorption performance of sludge biochar, and phosphomolybdic acid-modified sludge biochar was prepared at different temperatures. The results showed that the adsorption capacity of sludge biochar improved from 84.49 to 120.86 mg/g through modification with phosphomolybdic acid at 200 °C. The maximum adsorption capacities of phosphomolybdic acid-modified sludge biochar (200 °C pyrolysis temperature) at 298, 308, and 318 K were 283.87, 421.39, and 545.48 mg/g, respectively. Both liquid film and intraparticle diffusion were the main rate-limiting steps of tetracycline adsorption by phosphomolybdic acid-modified sludge biochar. Furthermore, the adsorption of tetracycline by phosphomolybdic acid-modified sludge biochar was mainly attributed to π-π interactions, electrostatic interactions, hydrogen bonding, and pore filling.

Strategic use of crop residue biochars for removal of hazardous compounds in wastewater

Crop residues are affordable lignocellulosic waste in the world, and a large portion of the waste has been burned, releasing toxic pollutants into the environment. Since the crop residue is a carbon and ingredient rich material, it can be strategically used as a sorptive material for (in)organic pollutants in the wastewater after thermo-chemical valorization (i.e., biochar production). In this review, applications of crop residue biochars to adsorption of non-degradable synthetic dyes, antibiotics, herbicides, and inorganic heavy metals in wastewater were discussed. Properties (porosity, functional groups, heteroatom, and metal(oxide)s, etc.) and adsorption capacity relationships were comprehensively reviewed. The current challenges of crop residue biochars and guidelines for development of efficient adsorbents were also provided. In the last part, the future research directions for practical applications of the crop residue biochars in wastewater treatment plants have been suggested.

Adsorption of heavy metal onto biomass-derived activated carbon: review

Due to the rapid development of the social economy and the massive increase in population, human beings continue to undertake processing, and commercial manufacturing activities of heavy metals, which has caused serious damage to the environment and human health. Heavy metals lead to serious environmental problems such as soil contamination and water pollution. Human health and the living environment are closely affected by the handling of heavy metals. Researchers must find several simple, economical and practical methods to adsorb heavy metals. Adsorption technology has been recognized as an efficient and economic strategy, exhibiting the advantages of recovering and reusing adsorbents. Biomass-derived activated carbon adsorbents offer large adjustable specific surface area, hierarchically porous structure, strong adsorption capacity, and excellent high economic applicability. This paper focuses on reviewing the preparation methods of biomass-derived activated carbon in the past five years. The application of representative biomass-derived activated carbon in the adsorption of heavy metals preferentially was described to optimize the critical parameters of the activation type of samples and process conditions. The key factors of the adsorbent, the physicochemical properties of the heavy metals, and the adsorption conditions affecting the adsorption of heavy metals are highlighted. In addition, the challenges faced by biomass-derived activated carbon are also discussed.

Feasible synthesis of bifunctional polysilsesquioxane microspheres for robust adsorption of Hg(II) and Ag(I): Behavior and mechanism

The pollution of Hg(II) and Ag(I) to water system exerts hazardous effect to aquatic ecosystem and public security. Simple strategy for constructing adsorbents to efficient remove them is greatly desired. Thus, a series of thiol and amino groups containing bifunctional polysilsesquioxanes (ASPSS) microspheres with adjustable porous structure and functional group content were synthesized by one-step feasible sol-gel process. The adsorption behavior and mechanism of ASPSS microspheres toward Hg(II) and Ag(I) was thoroughly determined. The maximum adsorption capacity of ASPSS for Hg(II) and Ag(I) are 4.32 and 3.86 mmol·g^-1 under 25 ℃. The as-prepared ASPSS microspheres can 100% selectively capture Hg(II) with the coexisting of Mn(II), Co(II), Pb(II), Cd(II), Cu(II), Fe(III). And they can 100% adsorb Ag(I) with the presence of Cd(II), Pb(II), Co(II), Ni(II), and Zn(II). Moreover, the ASPSS microspheres exhibit good removal efficiency for Hg(II) and Ag(I) from simulated industrial wastewater with the coexistence of multiple pollutants. Adsorption mechanism suggests the adsorption for Hg(II) and Ag(I) is the synergistic coordination effect of amino and thiol groups. The excellent adsorption selectivity for Hg(II) and Ag(I) is attributed to the super binding ability of these functional group. ASPSS microspheres also exhibit good regeneration ability and could be reused for removing Hg (II) and Ag(I) from aqueous solution with practical value.

Biochar application for greenhouse gas mitigation, contaminants immobilization and soil fertility enhancement: A state-of-the-art review

Rising global temperature, pollution load, and energy crises are serious problems, recently facing the world. Scientists around the world are ambitious to find eco-friendly and cost-effective routes for resolving these problems. Biochar has emerged as an agent for environmental remediation and has proven to be the effective sorbent to inorganic and organic pollutants in water and soil. Endowed with unique attributes such as porous structure, larger specific surface area (SSA), abundant surface functional groups, better cation exchange capacity (CEC), strong adsorption capacity, high environmental stability, embedded minerals, and micronutrients, biochar is presented as a promising material for environmental management, reduction in greenhouse gases (GHGs) emissions, soil management, and soil fertility enhancement. Therefore, the current review covers the influence of key factors (pyrolysis temperature, retention time, gas flow rate, and reactor design) on the production yield and property of biochar. Furthermore, this review emphasizes the diverse application of biochar such as waste management, construction material, adsorptive removal of petroleum and oil from aqueous media, immobilization of contaminants, carbon sequestration, and their role in climate change mitigation, soil conditioner, along with opportunities and challenges. Finally, this review discusses the evaluation of biochar standardization by different international agencies and their economic perspective.

Insights into the pH-Dependent Adsorption Behavior of Ionic Dyes on Phosphoric Acid-Activated Biochar

Activated biochar is a promising porous carbonaceous adsorbent material for organic pollutant removal, but it remains challenging to obtain high porosity and aromaticity through a simple and low-cost synthetic method. The common adsorption mechanisms of organic dyes on activated biochar should be further investigated in order to guide the synthesis of high-efficiency adsorbent materials. Here, we proposed a high-yield (up to 40 wt %) synthetic method of phosphoric acid-activated biochar from pomelo peel (PPC) with a high specific area of 877.3 m²/g through a facile thermal treatment at a relatively low temperature (250 °C). The specific activation mechanism of H₃PO₄ in the preparation of the adsorbent was investigated by a range of experiments and characterizations. The kinetic and isotherm experiments are also conducted to evaluate its dye adsorption behavior. According to the adsorption experiment results, PPC exhibits high saturated adsorption capacities for methyl orange (MO, 239.1 mg/g), rhodamine B (RhB, 2821.8 mg/g), methylene blue (MB, 580.5 mg/g), and crystal violate (CV, 396.6 mg/g) according to the Langmuir model. The maximum initial concentration of each dye solution for acquiring 90% removal efficiency is estimated to be 234.55 ppm (MO), 2943.8 ppm (RhB), 633.8 ppm (MB), and 423.6 ppm (CV) at 298 K with an adsorbent dosage of 1 g/L. The characterization results also indicate PPC has a complex synergetic mechanism for ionic dye adsorption behavior. This provides perspectives regarding PPC as a promising biochar adsorbent from biomass waste, which is probably useful for high-efficiency dye removal in water treatment.

Recycling Pomelo Peel Waste in the Form of Hydrochar Obtained by Microwave-Assisted Hydrothermal Carbonization

Pomelo peel (PP) is a kind of solid waste that is produced in the processing industry of honey pomelo. This study deeply explored the feasibility of recycling PP in the form of hydrochar (HC) by microwave-assisted hydrothermal carbonization (HTC) technology. Under the non-catalytic reaction conditions, the yield of hydrochar initially increased with the rise of reaction temperature (150-210 °C) until it remained relatively stable after 210 °C. Under the CaO-catalytical reaction condition, the yield of hydrochar did not change much at first (150-190 °C) but decreased significantly when the reaction temperature exceeded 190 °C. After the microwave-assisted HTC treatment, the PP-derived HC presented higher aromaticity, carbonization degree, porosity, and caloric value. Compared with raw PP, the nutrients in HC were more stable (conducive to being used as slow-release fertilizer). The application of CaO increased the pH value of HC and effectively promoted the accumulation of phosphorus in HC. The HC produced at 210 °C without any catalyst possessing a high devolatilization ability. Additionally, the HC obtained at 190 °C with CaO as the catalyst presented a high combustion property. In general, PP-derived HC showed great application potential in the field of soil remediation/improvement and solid fuels. This preliminary study would undoubtedly provide some important fundamental understanding of the microwave-assisted HTC of PP.

Remediation of heavy metal polluted waters using activated carbon from lignocellulosic biomass: An update of recent trends

The use of a cheap and effective adsorption approach based on biomass-activated carbon (AC) to remediate heavy metal contamination is clearly desirable for developing countries that are economically disadvantaged yet have abundant biomass. Therefore, this review provides an update of recent works utilizing biomass waste-AC to adsorb commonly-encountered adsorbates like Cr, Pb, Cu, Cd, Hg, and As. Various biomass wastes were employed in synthesizing AC via two-steps processing; oxygen-free carbonization followed by activation. In recent works related to the activation step, the microwave technique is growing in popularity compared to the more conventional physical/chemical activation method because the microwave technique can ensure a more uniform energy distribution in the solid adsorbent, resulting in enhanced surface area. Nonetheless, chemical activation is still generally preferred for its ease of operation, lower cost, and shorter preparation time. Several mechanisms related to heavy metal adsorption on biomass wastes-AC were also discussed in detail, such as (i) - physical adsorption/deposition of metals, (ii) - ion-exchange between protonated oxygen-containing functional groups (-OH, -COOH) and divalent metal cations (M²⁺), (iii) - electrostatic interaction between oppositely-charged ions, (iv) - surface complexation between functional groups (-OH, O^2-, -CO-NH-, and -COOH) and heavy metal ions/complexes, and (v) - precipitation/co-precipitation technique. Additionally, key parameters affecting the adsorption performance were scrutinized. In general, this review offers a comprehensive insight into the production of AC from lignocellulosic biomass and its application in treating heavy metals-polluted water, showing that biomass-originated AC could bring great benefits to the environment, economy, and sustainability.

Biochar raw material selection and application in the food chain: A review

As one of the largest carbon emitters, China promises to achieve carbon emissions neutrality by 2060. Various industries are developing businesses to reduce carbon emissions. As an important greenhouse gas emissions scenario, the reduction of carbon emissions in the food chain can be achieved by preparing the wastes into biochar. The food chain, as one of the sources of biochar, consists of production, processing and consumption, in which many wastes can be transferred into biochar. However, few studies use the food chain as the system to sort out the raw materials of biochar. A systematic review of the food chain application in serving as raw materials for biochar is helpful for further application of such technique, providing supportive information for the development of biochar preparation and wastes treating. In addition, there are many pollution sources in the food production process, such as agricultural contaminated soil and wastewater from livestock and aquatic, that can be treated on-site to achieve the goal of treating wastes with wastes within the food chain. This study focuses on waste resource utilization and pollution remediation in the food chain, summarizing the sources of biochar in the food chain and analyzing the feasibility of using waste in food chain to treat contaminated sites in the food chain and discussing the impacts of the greenhouse gas emissions. This review provides a reference for the resource utilization of waste and pollution reduction in the food chain.

Ball-milled bismuth oxybromide/biochar composites with enhanced removal of reactive red owing to the synergy between adsorption and photodegradation

In this paper, bismuth oxybromide (BiOBr)/biochar composites were synthesized by a facile ball milling method for synergistic adsorption and photodegradation of Reactive red 120 (RR120). The characterizations show that ball milling changed the degree of crystallization, increased the surface area, and promoted the charge transfer ability of biochar. The 70% BiOBr/BC composite showed the best removal efficiency for RR120 removal with or without light illumination, which proves its enhanced removal ability by adsorption and photodegradation. The biochar is served as a support of BiOBr for preventing its aggregation and a transporter of charges for promoting the separation of photo-induced carriers in composites. BiOBr can release the adsorption sites on the surface of composites by degradation, which facilitated the RR120 removal and regenerated the photocatalyst for reusing. The strong interactions between BiOBr and biochar in composites resulted from ball milling were beneficial for the charge transfer and synergistic removal of adsorption and degradation. Findings of this work indicate that ball milling method is an effective method to prepare highly efficient biochar-based composites for RR120 removal through synergistic adsorption and photodegradation.

Combing phosphorus-modified hydrochar and zeolite prepared from coal gangue for highly effective immobilization of heavy metals in coal-mining contaminated soil

Considering the adverse effects of heavy metals (HMs) on agriculture soil, in-situ immobilization has been paid great attention worldwide. P-modified biochar/hydrochar along with synthetic zeolite for efficient HMs immobilization in contaminated soil becomes a promising choice. In this study, H₃PO₄-modified hydrochar (BPH) derived from banana peels, and Na-X zeolite (ZL) prepared from coal gangue was applied individually and synergistically (1%BPH, 2%BPH 1%ZL, 2%ZL, and 1%BPH+1%ZL) to remediate a farmland soil polluted by Cd, Cu, and Pb near the coal-mining area. Compared with the mono-application of these two amendments, their combination significantly improved the soil organic carbon (SOC), electric conductivity (EC), and dehydrogenase activity. Besides, the addition of 1%CLH+1%ZL remarkably reduced the Cd, Cu, and Pb bioavailability by 67.01%, 57.01%, and 78.72%, respectively, in the soil after 100 d incubation by transforming these metals to more stable forms. The order of the HMs immobilization capacity for these two amendments was as follows: Pb > Cu > Cd. Moreover, the dominated immobilization mechanism of their synergistic application was that BPH could immobilize HMs by precipitation, complexation, and π-π electron-donor-acceptor interaction. The precipitation and complexation blocked the surface pores of BPH. The sustained release of phosphorus groups and radicals was prevented. This obstacle was possibly alleviated by adding ZL. Besides, the formation of cationic bridging, the enhancement of soil properties, and the physical adsorption of these amendments were also conducive to HMs immobilization in soil. This work indicated that co-application of BPH and ZL possibly was an excellent choice for immobilizing HMs in soil.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Biochar derived from fruit by-products using pyrolysis process for the elimination of Pb(II) ion: An updated review

Water pollution is one of the most concerning global environmental problems in this century with the severity and complexity of the issue increases every day. One of the major contributors to water pollution is the discharge of harmful heavy metal wastes into the rivers and water bodies. Without proper treatment, the release of these harmful inorganic waste would endanger the environment by contaminating the food chains of living organisms, hence, leading to potential health risks to humans. The adsorption method has become one of the cost-effective alternative treatments to eliminate heavy metal ions. Since the type of adsorbent material is the most vital factor that determines the effectiveness of the adsorption, continuous efforts have been made in search of cheap adsorbents derived from a variety of waste materials. Fruit waste can be transformed into valuable products, such as biochar, as they are composed of many functional groups, including carboxylic groups and lignin, which is effective in metal binding. The main objective of this study was to review the potential of various types of fruit wastes as an alternative adsorbent for Pb(II) removal. Following a brief overview of the properties and effects of Pb(II), this study discussed the equilibrium isotherms and adsorption kinetic by various adsorption models. The possible adsorption mechanisms and regeneration study for Pb(II) removal were also elaborated in detail to provide a clear understanding of biochar produced using the pyrolysis technique. The future prospects of fruit waste as an adsorbent for the removal of Pb(II) was also highlighted.

Passivation and remediation of Pb and Cr in contaminated soil by sewage sludge biochar tubule

Currently, numerous studies have carried out to research the effect of biochars remediation soil heavy metals (HMs) contaminated, but there have been fewer explorations of the effect of biochars tubule on soil HMs remediation. This work aimed to study the effect of passivation and remediation of lead (Pb) and chromium (Cr) contaminated soil after insert sewage sludge biochar (SSB) tubule. The results showed that the high risky fractions of Pb and Cr could be transformed into more stable fractions; also, Pb and Cr total contents are significantly decreased by SSB tubule. The mechanisms include adsorption, ion exchange, complexation, and precipitation which are concluded from the characteristic analysis. Detailly, the passivation of Pb and Cr is better when the moisture is 25% and 35%, respectively [Pb: exchangeable (F1), carbonate bound (F2) decreased by 25.1%, 16.8%, Fe-Mn oxides bound (F3) increased by 18.5%; Cr: F1 decreased by 73.0%, F2, F3, organic matter bound (F4) increased by 13.2%, 23.9%, 30.8%), respectively]. The remediation of Pb and Cr is better when the moisture is 25% and 35%, respectively, (Pb: decreased by 23.3%; Cr: decreased by 38.4%, respectively). The findings showed that the SSB tubule is effective when used for soil HMs contaminated.

One-Pot Synthesis of Nano CuO-ZnO Modified Hydrochar Derived from Chitosan and Starch for the H2S Conversion

A novel kind of hydrochar adsorbent, modified by CuO-ZnO and derived from chitosan or starch, was synthesized for H2S adsorption. The prepared adsorbent was characterized by BET, XRD, EDX, SEM, and XPS. The results showed that the modified hydrochar contained many amino groups as functional groups, and the nanometer metal oxide particles had good dispersion on the surface of the hydrochar. The maximum sulfur capacity reached 28.06 mg/g-adsorbent under the optimized conditions. The amine group significantly reduced the activation energy between H2S and CuO-ZnO conducive to the rapid diffusion of H2S among the lattices. Simultaneously, cationic polyacrylamide as a steric stabilizer could change the formation process of CuO and ZnO nanoparticles, which made the particle size smaller, enabling them to react with H2S sufficiently easily. This modified hydrochar derived from both chitosan and starch could be a promising adsorbent for H2S removal.

High-efficient removal of U(VI) from aqueous solution by self-assembly pomelo peel/palygorskite composite

The efficient separation of low-concentration radionuclides by the eco-friendly adsorbent is a compelling requirement in the development of nuclear industry. Hence, a novel composite consisted of one-dimensional palygorskite (Pal) and three-dimensional pomelo peel (PP) is prepared by self-assembly approach (PP/Pal) and coupling agent approach (PP/KPal) for removing uranium (U(VI)) from aqueous solution. Moreover, the mass ratio (PP/Pal), adsorbent dosage, pH, contact time, temperature, and ionic strength are investigated. Two adsorption kinetic models and isotherm models are used to investigate the kinetic behaviors and adsorption capacity, respectively. The maximum adsorption capacities were 370.5 mg·g^-1 on PP/Pal and 357.3 mg·g^-1 on PP/KPal at pH 6.0, contact time 150 min and 25 °C. Meanwhile, the composite can be easily separated from water via a simple filtering. Furthermore, thermodynamic parameters indicate that adsorption is an endothermic and spontaneous process. And the surface complexation, ion exchange, and electrostatic attraction play a vital role. This work shows that the PP/Pal composite with high efficiency, low cost, and green has a further application in the treatment of wastewater containing U(VI).

Utilization of pomelo peels to manufacture value-added products: A review

Pomelo peel as a by-product from pomelo consumption is rich in various nutrients and functional compounds, while most of the by-product is disposed as wastes. The utilization of pomelo peels could not only result in valued-added products/ingredients, but also reduce the environmental threats. By mainly reviewing the recent articles, pomelo peels could be directly used to produce candied pomelo peel, tea, jams, etc. Additionally, functional components (essential oils, pectin, polyphenols, etc.) could be extracted from pomelo peels and applied in food, pharmaceutical and chemical fields. The extraction methods exerted important influences on the composition, physicochemical properties, bioactivities and structures of the resultant fractions. Furthermore, pomelo peel was exploited to make adsorbents, bioethanol, etc. For the future investigations, the functionality- or bioactivity-oriented regimes to recovery valuable components from pomelo peel should be developed in an economic, effective and eco-friendly way and their applicability in large-scale production should be addressed.

Facile preparation of sulfonated biochar for highly efficient removal of toxic Pb(II) and Cd(II) from wastewater

Biochar is deemed as the ideal material for the effective removal of heavy metals in wastewater treatment. Herein, we developed a facile one-step solvothermal method for the preparation of sulfonated biochar (SBC) from Axonopus compressus under a low-temperature condition. FTIR and XPS analysis demonstrate that plenty of -OH, -COOH and -SO₃H moieties are generated on the surface of SBC during the sulfonation process. Due to high electronegativity and strong complexation of these moieties, SBC can rapidly adsorb Pb(II) and Cd(II) with capacities of 191.07 and 85.76 mg/g respectively within 5 min. SBC can be reused for 5 cycles with a negligible loss of adsorption capacity. In addition, different biomass-based biochars are prepared under the identical experimental conditions, and they are successfully applied in the treatments of Pb(II) and Cd(II). The satisfying results indicate that one-step low-temperature sulfonation could be a universal method, and various types of biomass waste could be the abundant, effective, economical material source for the treatment of environmental heavy metal pollution in future.

Effects of aging and weathering on immobilization of trace metals/metalloids in soils amended with biochar

Biochar is an effective amendment for trace metal/metalloid (TMs) immobilization in soils. The capacity of biochar to immobilize TMs in soil can be positively or negatively altered due to the changes in the surface and structural chemistry of biochar after soil application. Biochar surfaces are oxidized in soils and induce structural changes through physical and biochemical weathering processes. These changes in the biochar surface and structural chemistry generally increase its ability to immobilize TMs, although the generation of dissolved black carbon during weathering may increase TM mobility. Moreover, biochar modification can improve its capacity to immobilize TMs in soils. Over the short-term, engineered/modified biochar exhibited increased TM immobilization capacity compared with unmodified biochar. In the long-term, no large distinctions in such capacities were seen between modified and unmodified biochars due to weathering. In addition, artificial weathering at laboratories also revealed increased TM immobilization in soils. Continued collection of mechanistic evidence will help evaluate the effect of natural and artificial weathering, and biochar modification on the long-term TM immobilization capacity of biochar with respect to feedstock and synthesis conditions in contaminated soils.

A critical review of the production and advanced utilization of biochar via selective pyrolysis of lignocellulosic biomass

Biochar is a carbon-rich product obtained from the thermo-chemical conversion of biomass. Studying the evolution properties of biochar by in-situ modification or post-modification is of great significance for improving the utilisation value of lignocellulosic biomass. In this paper, the production methods of biochar are reviewed. The effects of the biomass feedstock characteristics, production processes, reaction conditions (temperature, heating rate, etc.) as well as in-situ activation, heteroatomic doping, and functional group modification on the physical and chemical properties of biochar are compared. Based on its unique physicochemical properties, recent research advances with respect to the use of biochar in pollutant adsorbents, catalysts, and energy storage are reviewed. The relationship between biochar structure and its application are also revealed. It is suggested that a more effective control of biochar structure and its corresponding properties should be further investigated to develop a variety of biochar for targeted applications.

Biochar technology in wastewater treatment: A critical review

Biochar is a promising agent for wastewater treatment, soil remediation, and gas storage and separation. This review summarizes recent research development on biochar production and applications with a focus on the application of biochar technology in wastewater treatment. Different technologies for biochar production, with an emphasis on pre-treatment of feedstock and post treatment, are succinctly summarized. Biochar has been extensively used as an adsorbent to remove toxic metals, organic pollutants, and nutrients from wastewater. Compared to pristine biochar, engineered/designer biochar generally has larger surface area, stronger adsorption capacity, or more abundant surface functional groups (SFG), which represents a new type of carbon material with great application prospects in various wastewater treatments. As the first of its kind, this critical review emphasizes the promising prospects of biochar technology in the treatment of various wastewater including industrial wastewater (dye, battery manufacture, and dairy wastewater), municipal wastewater, agricultural wastewater, and stormwater. Future research on engineered/designer biochar production and its field-scale application is discussed. Based on the review, it can be concluded that biochar technology represents a new, cost effective, and environmentally-friendly solution for the treatment of wastewater.

Magnetic Fe3O4 Nanoparticle Biochar Derived from Pomelo Peel for Reactive Red 21 Adsorption from Aqueous Solution

In this study, Fe3O4 nanoparticle-loaded biochar derived from the pomelo peel (FO-PPB) was synthesized and applied as an affordable material for the adsorption of Reactive Red 21 (RR21) in an aqueous solution. The characteristics of FO-PPB were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), Raman spectra, Fourier transform infrared spectra (FTIR), and Brunauer–Emmett–Teller (BET) surface area. The adsorption process of FO-PPB with RR21 was evaluated through batch experiments to examine various parameters including solution pH, contact time, adsorbent dose, initial RR21 concentration, and solution temperature. Results show that FO-PPB produced by the impregnation ratio between iron (Fe) and pomelo peel biochar (PPB) of 5 : 1 (w/w) had the best adsorption performance. The adsorption capacities of PPB and FO-PPB at optimum experimental conditions (solution pH 3, contact time of 60 min, solution temperature of 40°C, initial RR21 concentration of 300 mg/L, and adsorbent dose of 2 g/L) were 18.59 and 26.25 mg/g, respectively. The adsorption isotherms of RR21 on PPB and FO5-PPB were described well by Langmuir and Sips models with high R2 values of 0.9826 and 0.9854 for FO5-PPB and 0.9701 and 0.9903 for PPB, respectively. The obtained data also well matched the pseudo-first-order and pseudo-second-order models with R2 values ≥ 0.96. Chemisorption through sharing or electronic exchange was determined as the main adsorption mechanism.

Insights into facile synthesized pomelo biochar adsorbing thallium: potential remediation in agricultural soils

Little information is available on thallium (Tl) adsorption onto fruit-derived biochar. In this study, pomelo peel and waste pomelo were thus chosen to prepare two kinds of biochars recorded as PPB and WPB. The two produced biochars subsequently evaluated their potential remediation of thallium (Tl) contamination in agricultural soils by their Tl adsorption capacity. Results showed that the two pomelo-derived biochars presented obvious microporous structure and rich oxygen-containing functional group, supported by the observant data of specific surface area, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Furthermore, Langmuir isothermal adsorption model can better fit the adsorption behavior of thallium onto PPB and WPB, and the subsequent maximum adsorption capacity was 4283.9 μg g^-1 and 5286.0 μg g^-1, respectively. In addition, the pseudo-second-order kinetic model could well fit the kinetic behavior of thallium adsorption onto PPB and WPB, indicating that the process is accompanied by chemical adsorption. Meanwhile, in agricultural soils, PPB and WPB can be used as environmentally friendly adsorbents to remediate Tl contamination due to their pH increase of the tested soils and their comparable adsorption ability of Tl. The obtained findings can provide insights into comprehensively developed fruit-derived biochar technology to remediate Tl contamination in agricultural soils.

Enhanced phosphate removal from aqueous solution using resourceable nano-CaO2/BC composite: Behaviors and mechanisms

The situation of eutrophication and shortage of phosphorus resources have triggered the development of new methods for the removal and recovery of phosphorus. In this study, a novel and highly efficient composite (nano-CaO₂/BC) was fabricated by using the porous biochar (BC) to load calcium peroxide (CaO₂) nanoparticles. The developed nano-CaO₂/BC was applied to remove and recover phosphate from P-contained sewage. The phosphate removal performance of the composite was examined using the bulk solutions with different pH values, coexisting anions, composite dosages, and initial phosphate concentrations. The phosphate adsorption was a typical chemisorption process that agreed well with the pseudo-second-order kinetic model. Isotherm studies showed that the adsorption matched well with Langmuir-Freundlich and the maximum adsorption capacity at equilibrium was 213.22 ± 13.57 mg g^-1 (298 K). The characterization results demonstrated that the predominant adsorption mechanism was precipitation. Moreover, the composite had good reusability. The seedling growth test confirmed that the P-laden composite can be mixed with soil to promote the growth of seedlings. Therefore, the method of "cycle back to soil" of used composite provided a way of resource utilization and waste disposal.

Recycling supercapacitor activated carbons for adsorption of silver (I) and chromium (VI) ions from aqueous solutions

In this study, we reported on the recycling of carbon materials from spent commercial supercapacitors and its application as low-cost adsorbent for high-efficiency removal of Ag(I) and Cr(VI) ions from aqueous solutions. Adsorption kinetics and isotherms, and effects of initial pH were carried out to investigate the adsorption performance of the recycled supercapacitor activated carbon (RSAC), whereas a series of characterizations such as SEM, EDX, BET, XPS, XRD and FTIR were employed to detailedly analyse the adsorption mechanism. The RSAC showed maximal adsorption capacity for Ag(I) and Cr(VI) of 104.0 and 96.3 mg g^-1, respectively, with adsorbent dosage of 2 g L^-1 and initial ions concentration of ∼2000 mg L^-1 at room temperature (23 ± 1 °C), and the adsorption was rapid and influenced by the initial pH value. The outstanding adsorption performance of RSAC was attributed to the high specific surface area (1403 m² g^-1) and abundant multifarious oxygenic groups which could participate in the electrostatic attraction and reduction reaction of Ag(I) and Cr(VI) during the adsorption process. Furthermore, the predominate species of the adsorbed toxic Ag(I) and Cr(VI) on the surface of RSAC was metallic silver particle (about 2 μm) and harmless Cr(III), respectively, thus it was possible for further recycling and disposal.

Preparation of Sodium Humate-Modified Biochar Absorbents for Water Treatment

Some chemical substances could improve the sorption capacity of biochars. In this paper, sodium humate was introduced to the pyrolysis of two biomass samples at 600 °C, and sodium humate-biochars have been successfully synthesized. The surface area and surface morphologies of all of the biochars were characterized, and the results indicated that sodium humate-biochars have higher surface areas, and sodium humate particles were grown on the surfaces of the biochars. Adsorption isotherm and kinetics of methylene blue (MB) onto the biochars were carried out by batch adsorption experiments. The results suggested that incorporation of sodium humate could increase the adsorption capacity of MB onto the biochars (from 10.79 to 16.21, 8.62 to 11.03 mg/g for peanut shells and white clover residues, respectively). The adsorption experimental results also suggest that the adsorption process of MB onto sodium humate-biochars is controlled by both intraparticle diffusion and film diffusion. As a whole, this work probes the possibility of sodium humate to modify the surface of biochar and improve its adsorption ability with contaminants.

Shaddock peels-based activated carbon as cost-saving adsorbents for efficient removal of Cr (VI) and methyl orange

A simple and economical method was proposed to synthesize the shaddock peels-based activated carbon (SPAC) for their application as efficient sorbents to eliminate Cr (VI) and methyl orange (MO) from one-component and two-component systems. The synthesis was conducted via activation of phosphoric acid and high-temperature carbonization. The as-prepared SPAC was characterized by Brunauer-Emmett-Teller, scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, X-ray diffraction, and Fourier transform infrared spectroscopy, among other techniques. The adsorption experiment, which used five types of fruit peel (shaddock peels, orange peels, apple peels, banana peels, and tangerine peels), indicated that shaddock peels were the optimal precursors, with the high removal efficiencies for Cr (VI) (21.2%) and MO (54.25%). The effects of various factors (e.g., initial concentration, sorbent dosage, pH values, and contact time) were systematically evaluated. For the one-component system, the maximum adsorption capacities of Cr (VI) (9.95 mg/g) and MO (94.59 mg/g) reached pH levels 2 and 3, respectively. Kinetic modeling demonstrated that the pseudo-second-order kinetic model was adopted for the one-component and two-component systems. Isotherm studies suggested that Cr (VI) and MO sorption processes in the one-component explained well the Langmuir and Freundlich models, respectively. The extended Freundlich multicomponent isotherm model was more compatible for explaining competitive adsorption in the binary component system. The adsorbed amount of Cr (VI) was markedly suppressed by MO, whereas MO adsorption was not significantly influenced owing to the existence of Cr (VI). The higher adsorption capacity of MO could be mainly attributed to the strong force acting between MO and SPAC. The findings of this study confirmed that SPAC provided a sustainable choice for cycling solid waste shaddock peels to remove hazardous contaminants.