A novel PEI-grafted N-doping magnetic hydrochar for enhanced scavenging of BPA and Cr(VI) from aqueous phase

Sustainable hydrochar as an efficient persulfate activator for cost-effective degradation of bisphenol A

This study explored Mason pine-derived hydrochar (MPHC) as an effective adsorbent and persulfate (PS) activator for degrading bisphenol A (BPA). Increasing MPHC dosage from 0.25 to 2.0 g L-1 raised BPA removal from 42% to 87%. Similarly, at the same MPHC dosage range and fixed PS concentration (8 mM), BPA removal by MPHC/PS increased from 66% to 91%. Additionally, at a fixed MPHC dosage (1.0 g L-1), higher PS concentrations (2-32 mM) resulted in an overall BPA removal increase from 78% to 99%. The optimal pH for BPA removal by MPHC was at pH 3, while for MPHC/PS was at pH 9. BPA degradation by MPHC was optimal at pH 3, whereas MPHC/PS was at pH 3 and pH 9. Additionally, pH 7 favored BPA adsorption for both MPHC and MPHC/PS. The study also considered the influence of coexisting anions and humic acid (HA). PO43- and NO3- influence adsorption on MPHC, but these anions' effect on MPHC/PS is limited. Furthermore, the existence of HA had minimal influence on BPA removal by MPHC/PS. The contributions of different reactive species by MPHC for BPA degradation are as follows: electron-hole (h+) 2%, singlet oxygen (1O2) 7%, superoxide radicals (O2•-) 13%, electron (e-) 2%, hydroxyl radical (•OH) 3%, whereas the remaining 48% removal was the contribution of adsorption. For MPHC/PS, adsorption accounted for 39 %, more reactive species were involved in degradation, and the donations are (h+) 3%, sulfate radicals (SO4•-) 3%, (1O2) 19%, (O2•-) 15%, (e-) 2%, and (•OH) 2%. Additionally, the performance of MPHC remains stable after three operational cycles. The preparation cost of MPHC is 3.01 € kg-1. These results highlight the potential of MPHC as an environmentally friendly material for activating PS and removing organic pollutants, suggesting its promising application in future environmental remediation efforts.

Efficient removal of Chromium(VI) from wastewater based on magnetic multiwalled carbon nanotubes coupled with deep eutectic solvents

Industrial wastewater containing heavy metal Cr(VI) seriously affects the health of organisms and may even lead to cancer. Developing efficient adsorbents that can quickly separate heavy metals is crucial for treating wastewater. In this study, magnetic multiwalled carbon nanotubes (MMWCNTs) with moderate particle size and abundant surface active sites were prepared by coating multiwalled carbon nanotubes with magnetic nanoparticles. The results of FTIR, XRD, TG, VSM, BET, and EDS showed MWCNTs completely encapsulated on the surface of the magnetic nanoparticles, with a particle size of approximately 30 nm. Oxygenated groups provided abundant surface active sites and formed numerous mesopores. The response surface methodology was used to optimize the adsorbent dose, adsorption contact time and adsorption temperature, and the removal rate of Cr(VI) was more than 95%. The quasi-second order kinetics and Freundlich adsorption isotherm model explained the adsorption process to Cr(VI). MMWCNTs interacted with Cr(VI) through electrostatic attraction, reduction reactions, complexation, and other means. The extensive hydrogen bonding of the green solvent deep eutectic solvent (DES) was employed to desorb the MMWCNTs and desorption rate exceed 90%. Even after five adsorption-regeneration cycles, the adsorbent maintained a high capacity. In conclusion, these novel MMWCNTs, as efficient adsorbents paired with DES desorption, hold broad potential for application in the treatment of Cr(VI)-contaminated wastewater.

Green synthesis of magnetic azo-linked porous organic polymers with recyclable properties for enhanced Bisphenol-A adsorption from aqueous solutions

Porous organic polymers (POPs) present superior adsorption performance to steroid endocrine disruptors. However, the effective recovery and high cost have been a big limitation for their large-scale applications. Herein, magnetic azo-linked porous polymers (Fe3O4@SiO2/ALP-p) were designed and prepared in a green synthesis approach using low-price materials from phloroglucinol and pararosaniline via a diazo-coupling reaction under standard temperature and pressure conditions, which embedded with Fe3O4@SiO2 nanoparticles to form three-dimensional interlayer network structure with flexible-rigid interweaving. The saturated adsorption capacity to bisphenol-A (BPA) was 485.09 mg/g at 298 K, which increased by 1.4 times compared with ALP-p of relatively smaller mass density. This enhanced adsorption was ascribed to increment from surface adsorption and pore filling with 2.3 times of specific surface area and 2.6 times of pore volume, although the total organic functional groups decreased with Fe3O4@SiO2 amendment. Also, the adsorption rate increased by about 1.1 and 1.5-fold due to enhancement in the initial stage of surface adsorption and subsequent stage pore diffusion, respectively. Moreover, this adsorbent could be used in broad pH (3.0-7.0) and salinity adaptability (<0.5 mol/L). The loss of adsorption capacity and magnetic recovery were lower than 1.1% and 0.8% in each operation cycle because of the flexible-rigid interweave. This excellent performance was contributed by synergistic effects from physisorption and chemisorption, such as pore filling, electrostatic attraction, π-π stacking, hydrogen bonding, and hydrophobic interaction. This study offered a cost-effective, high-performing, and ecologically friendly material along with a green preparation method.

Biodegradation of atrazine with biochar-mediated functional bacterial biofilm: Construction, characterization and mechanisms

The abuse and residue of herbicides in the black soil area had seriously affected the soil structure, function and crop growth, posing severe threats to agricultural soil environment and public health. Given the limitation of routine microbial remediation, innovative and eco-friendly functional bacterial biofilm which could adapt under adverse conditions was developed on the biochar to investigate its enhanced bioremediation and metabolic characteristics of typical herbicide atrazine. Results revealed that the atrazine degrading strain Acinetobacter lwoffii had competitive advantage in soil indigenous microorganisms and formed dense biofilms on the biochar which was beneficial to cell viability maintenance and aggregations. Metatranscriptomics and RT-qPCR analysis demonstrated that the biochar-mediated biofilm improved the frequency of intercellular communications through quorum sensing and two-component signal regulation systems, and enhanced the atrazine biodegradation efficiency through horizontal gene transfer in co-metabolism mode, providing important scientific basis for the biological remediation of farmland soil non-point source pollution.

Biochar mediated high-rate anaerobic bioreactors: A critical review on high-strength wastewater treatment and management

Treatment of high-strength wastewater is critical for the aquatic environment and receiving water bodies around the globe. Untreated or partially treated high-strength wastewater may cause severe damage to the existing water bodies. Various high-rate anaerobic bioreactors have been developed in the last decades for treating high-strength wastewater. High-rate anaerobic bioreactors are effective in treating industrial wastewater and provide energy in the form of methane as well. However, the physical or chemical properties of high-strength industrial wastewater, sometimes, disrupt the functioning of a high-rate anaerobic bioreactor. For example, the disintegration of granular sludge in up flow anaerobic sludge blanket reactor or membrane blocking in an anaerobic membrane bioreactor are the results of a high-strength wastewater treatment which hamper the proper functioning and may harm the wastewater treatment plant economically. Biochar, if added to these bioreactors, may help to alleviate the ill-functioning of high-rate anaerobic bioreactors. The primary mechanisms by biochar work in these bioreactors are direct interspecies electron transfer, microbial immobilization, or gene level alternations in microbial structure. The present article explores and reviews the recent application of biochar in a high-rate anaerobic bioreactor treating high-strength industrial wastewater.

One-step synthesis of ferrous disulfide and iron nitride modified hydrochar for enhanced adsorption and reduction of hexavalent chromium in Bacillus LD513 by promoting electron transfer and microbial metabolism

Microbial immobilization technology is effective in improving bioremediation efficiency and heavy metal pollution. Herein, Bacillus LD513 with hexavalent chromium (Cr(VI)) tolerance was isolated and immobilized on a novel ferrous disulfide (FeS2)/iron nitride (FeN) modified hydrochar (Fe3-SNHC) prepared from waste straws. The prepared Fe3-SNHC-based LD513 (FeLD) significantly improves Cr(VI) adsorption and reduction by 31.4 % and 15.7 %, respectively, compared to LD513 alone. Furthermore, the FeLD composite system demonstrates efficient Cr(VI) removal efficiency and good environmental adaptability under different culture conditions. Microbial metabolism and electrochemical analysis indicate that Fe3-SNHC is an ideal carrier for protecting LD513 activity, promoting extracellular polymer secretion, and reducing oxidative stress. Additionally, the carrier serves as an electron shuttle that accelerates electron transfer and promotes Cr(VI) reduction. Overall, FeLD is an environmentally friendly biocomposite that shows good promise for reducing Cr(VI) contamination in wastewater treatment.

Integrating metal-organic framework ZIF-8 with green modifier empowered bacteria with improved bioremediation

Suspended microorganisms often experience diminished efficacy in the bioremediation of polycyclic aromatic hydrocarbons (PAHs). In this study, the potential of zeolite imidazolate framework-8 (ZIF-8) and the eco-friendly modifier citric acid (CA) was harnessed to generate a biomimetic mineralized protective shell on the surface of Bacillus subtilis ZL09-26, resulting in an enhanced capability for PAH degradation. This investigation encompassed the integrated responses of B. subtilis ZL09-26 to ZIF-8 and ZIF-8-CA at both cellular and proteomic levels. The amalgamation of ZIF-8 and CA not only stimulated the growth and bolstered the cell viability of B. subtilis ZL09-26, but also counteracted the toxic effects of phenanthrene (PHE) stress. Remarkably, the bioremediation prowess of B. subtilis ZL09-26@ZIF-8-CA surpassed that of ZL09-26@ZIF-8 and ZL09-26, achieving a PHE removal rate of 94.14 % within 6 days. After undergoing five cycles, ZL09-26@ZIF-8-CA demonstrated an enduring PHE removal rate exceeding 83.31 %. A complex interplay of various metabolic pathways orchestrated cellular responses, enhancing PHE transport and degradation. These pathways encompassed direct PHE biodegradation, central carbon metabolism, oxidative phosphorylation, purine metabolism, and aminoacyl-tRNA biosynthesis. This study not only extends the potential applications of biomineralized organisms but also offers alternative strategies for effective contaminant management.

Effective adsorption of bisphenol A from aqueous solution using phosphoric acid-assisted hydrochar

Sycamore leaf biochar (PSAC) was prepared by a two-step phosphoric acid-assisted hydrothermal carbonization combined with a short-time activation method. The characterization results showed that the introduction of phosphoric acid molecules and thermal activation resulted in a substantial increase in the specific surface area (994.21 m2/g) and microporous capacity (0.307 cm3/g) of PSAC. The batch adsorption results showed that the adsorption process of PSAC on bisphenol A (BPA) was best described by the pseudo-second-order kinetic model and Sips isothermal model, with a maximum adsorption capacity of 247.42 mg/g. The adsorption of BPA onto PSAC was determined to be a spontaneous endothermic process. The equilibrium adsorption capacity of PSAC exhibited an upward trend with increasing initial BPA concentration and temperature while decreasing with higher adsorbent dosage and pH value. Coexisting cations and humic acids in water have little impact on the adsorption performance of PSAC for BPA. The adsorption mechanism of BPA by PSAC was mainly governed by pore filling and hydrogen bonding interactions, π-π interactions, and intraparticle diffusion. Furthermore, PSAC demonstrated good reusability by its sustained adsorption capacity of BPA, which remained at 82.6% of the initial adsorption capacity even after four adsorption-desorption cycles. These findings highlight the potential of utilizing low-cost sycamore leaf biochar as an effective adsorbent for the removal of the endocrine disruptor BPA.

Cellulose cryogels from herbal residues for oily wastewater purification

Recycling herbal residues for oily wastewater purification is a potential way to use the wastes to treat wastes. Cellulose extracted from herbal residues is a fine material for cryogel fabrication. However, the cellulose cryogels were not suitable for oily wastewater treatment due to their amphiphilicity. To address this issue, the cryogels were modified with methyltrimethoxysilane (MTMS), which made them hydrophobic and reduced their surface energy. In this study, the herbal residues (Ficus microcarpa L. f) were used in cryogel preparation for the first time. The cryogels exhibit super lightweight and low density. The modified cryogels show excellent sorption capacity for free oils, especially silicone oil (51.22 g/g), and outperformed some recent sorbents. They also effectively separated water-in-toluene emulsion stabilized by Span 80, with a separation efficiency of 98.57 % and a flux of 1474.67 L/m2h. This study demonstrated a novel application of waste herbal residues in the field of environmental remediation.

Trithiocyanurate-functionalized hydrochar for effectively removing methylene blue and Pb (II) cationic pollutants

Functionalization can change the physicochemical properties of hydrochar and improve its ability to adsorb pollutants. Herein, a trithiocyanurate-functionalized hydrochar (TTHC) was obtained from acylation of chloroacetyl chloride and hydrochar and modification with trithiocyanuric acid in alkaline conditions. TTHC can efficiently remove cationic methylene blue (MB) and Pb(II) from wastewater. The removal can be expressed with pseudo-second-order kinetic and Langmuir models. The MB and Pb(II) removed uptakes by TTHC at 298 K exceeded 909.9 and 182.8 mg g-1 respectively, and the removal rates reached 90% and 98% within 120 min respectively. Characterizations show TTHC is functionalized with trithiocyanurate, and rich in thiolate and aromaticity, and tends to adsorb MB/Pb(II) via multiple adsorption mechanisms. After five sorption-desorption regeneration cycles, TTHC maintained 80% and 99% adsorption capacities for MB and Pb(II) respectively. Therefore, TTHC is a promising efficient sorbent for removing MB and Pb(II) from effluents.

Ferrous disulfide and iron nitride sites on hydrochar to enhance synergistic adsorption and reduction of hexavalent chromium

In this study, a novel hydrochar containing ferrous disulfide (FeS2) and iron nitride (FeN) was prepared via a one-pot hydrothermal method to enhance the synergistic adsorption and reduction of hexavalent chromium (Cr(VI)). This material (Fe3-SNHC) exhibited a Cr(VI) removal capacity of 431.3 mg·g-1 and high tolerance to coexisting anions at pH 2. Adsorption occurred via monolayer chemisorption. Variation in material structure and density functional theory calculations proved that multiple active sites formed by interactions between heteroatoms improved the chemical inertness of hydrochar. FeN and FeS2 with two electron-donating groups had strong reducing ability to facilitate the conversion of Cr(VI) to trivalent chromium. It was concluded that next to electrostatic adsorption and complexation, synergistic reduction among multiple active sites were the dominant mechanisms involved in the removal Cr(VI). This study shows that Fe3-SNHC is a promising and environment-friendly material for Cr(VI) to remove it from wastewater.

Adsorption properties of active biochar: Overlooked role of the structure of biomass

Vascular plants account for more than 80% of all biomass on earth and are potential precursors of biochar. However, the changes of vascular bundle have received less attention during the preparation of biochar. In this study, loofah sponge (LS), tangerine pith (TP), and rhodiola rosea (RR), were selected to show the role of vascular bundle in biochar through the pretreatment of vascular bundle. The results showed that the active biochar prepared with vascular bundle protection had high adsorption capacity for methylene blue (LS: 953.53 mg/g, TP: 714.77 mg/g, RR: 583.49 mg/g). The Brunauer-Emmett-Teller method was used to measure the specific surface area (SSA) of active biochar. The SSA of LS active biochar prepared by vascular bundle protection was 2262.67 m2/g, and has high adsorption properties under different conditions. In conclusion, the protection of vascular bundle during biochar preparation is important to improve the utilization of biological resources and environmental adsorption.

Microwave-assisted one-pot preparation of magnetic cactus-derived hydrochar for efficient removal of lead(Ⅱ) and phenol from water: Performance and mechanism exploration

A novel magnetic hydrochar derived from cactus cladode (MW-MHC) was successfully synthesized through one-pot microwave-assisted process for efficiently removing lead(Pb)(Ⅱ) and phenol. From batch adsorption experiments, MW-MHC possessed the highest uptake amounts for Pb(Ⅱ) and phenol of 139.34 and 175.32 mg/g within 20 and 60 min, respectively. Moreover, the removal of Pb(Ⅱ) and phenol by MW-MHC remained essentially stable under the interference of different co-existing cations, presenting the excellent adaptability of MW-MHC. After three cycles of regeneration experiments, MW-MHC still had preferable adsorption performance and could be easily recycled, indicating its excellent reusability. Significantly, the uptake mechanisms of Pb(Ⅱ) on MW-MHC were regarded as chemical complexation, pore filling, precipitation, and electrostatic attraction. Meanwhile, the phenol uptake might be dominated by π-π interaction and hydrogen bonding. The above consequences revealed that MW-MHC with high removal performance was a promising adsorbent for remediating wastewater containing heavy metals and organics.

From Waste to Resource: Valorization of Lignocellulosic Agri-Food Residues through Engineered Hydrochar and Biochar for Environmental and Clean Energy Applications-A Comprehensive Review

Agri-food residues or by-products have increased their contribution to the global tally of unsustainably generated waste. These residues, characterized by their inherent physicochemical properties and rich in lignocellulosic composition, are progressively being recognized as valuable products that align with the principles of zero waste and circular economy advocated for by different government entities. Consequently, they are utilized as raw materials in other industrial sectors, such as the notable case of environmental remediation. This review highlights the substantial potential of thermochemical valorized agri-food residues, transformed into biochar and hydrochar, as versatile adsorbents in wastewater treatment and as promising alternatives in various environmental and energy-related applications. These materials, with their enhanced properties achieved through tailored engineering techniques, offer competent solutions with cost-effective and satisfactory results in applications in various environmental contexts such as removing pollutants from wastewater or green energy generation. This sustainable approach not only addresses environmental concerns but also paves the way for a more eco-friendly and resource-efficient future, making it an exciting prospect for diverse applications.

Elaborating the mechanism of lead adsorption by biochar: Considering the impacts of water-washing and freeze-drying in preparing biochar

This paper examined the impacts of different pretreatments on the characteristics of biochar and its adsorption behavior for Pb2+. Biochar with combined pretreatment of water-washing and freeze-drying (W-FD-PB) performed a maximum adsorption capacity for Pb2+ of 406.99 mg/g, higher than that of 266.02 mg/g on water-washing pretreated biochar (W-PB) and 188.21 mg/g on directly pyrolyzed biochar (PB). This is because the water-washing process partially removed the K and Na, resulting in the relatively enriched Ca and Mg on W-FD-PB. And the freeze-drying pretreatment broke the fiber structure of pomelo peel, favoring the development of a fluffy surface and large specific surface area during pyrolysis. Quantitative mechanism analysis implied that cation ion exchange and precipitation were the driving forces in Pb2+ adsorption on biochar, and both mechanisms were enhanced during Pb2+ adsorption on W-FD-PB. Furthermore, adding W-FD-PB to Pb-contaminated soil increased the soil pH and significantly reduced the availability of Pb.

Facile one-step synthesis of a versatile nitrogen-doped hydrochar from olive oil production waste, "alperujo", for removing pharmaceuticals from wastewater

In line with the principles of zero waste and recycling, alperujo (AL) was used in this study to produce a value-added product: hydrochar (HC) with high adsorption capacity. An optimization of the hydrothermal carbonization (HTC) conditions, such as temperature, residence time, and water/solid ratio, was carried out to maximize the adsorption capacity. Eight HCs were obtained, and an in-depth comparative characterization, as well as adsorption tests of two pharmaceuticals with very different physicochemical properties (fluoxetine (FLX) and cefazolin (CFZ)), were performed. This first step allowed for elucidation of the best candidates to carry out nitrogen grafting on their surface, resulting in the HC obtained at a higher water/solid ratio and temperature, and longer residence time: 3-220ºC-2.5 h with a maximum uptake of 4.6 and 0.4 mg/g for FLX and CFZ, respectively. After that, a facile one-step, one-pot synthesis of nitrogen-doped hydrochars (N-HC) was developed to prepare a versatile bio-adsorbent with enhanced adsorption capacity. Two N-HCs were prepared using urea (U-HC) and polyethyleneimine (PEI-HC) and were intensively characterized to shed light on the adsorption mechanism. In both cases, amide groups were formed, which favored the adsorption process. PEI-HC acquired an outstanding maximum adsorption capacity of 983.84 mg/g for CFZ, and 29.31 mg/g for FLX, and the process was well described by the Freundlich isotherm and pseudo-second-order kinetic model. A co-adsorption test was performed using PEI-HC for both pharmaceuticals, finding that the adsorption process occurs in different active sites because there was no interference between the pollutants. This fact corroborates the versatility of the new bio-adsorbent synthesized.

The binding mechanism of benzophenone-type UV filters and human serum albumin: The role of site, number, and type of functional group substitutions

Benzophenone-type UV filters (BPs) are common in natural aquatic environments. They can cause endocrine disruption or other adverse effects once they enter the human body via the food chain or drinking water. The primary cause of BPs accumulation and toxicity is the transport of BPs into the human body. Functional group substitutions can have a significant impact on the interactions of BPs and transporters, resulting in a variety of impact effects. Therefore, we explored the interaction between human serum albumin (HSA, a typical transporter) and ten typical BPs [benzophenone (BP1), 2-hydroxybenzophenone (BP2), 4-hydroxybenzophenone (BP3), 2,2'-dihydroxybenzophenone (BP4), 2,4-dihydroxybenzophenone (BP5), 4,4'-dihydroxybenzophenone (BP6), 2,4,4'-trihydroxybenzophenone (BP7), 2,2',4,4'-tetrahydroxybenzophenone (BP8), 2-hydroxy-4-methoxybenzophenone (BP9), and 2,2'-dihydroxy-4-methoxybenzophenone (BP10)] to study the role of functional group substitutions in binding. The results showed that BPs could bind to HSA at site 2, with binding constants ranging from 2.01 × 10³ to 4.57 × 10⁵ L/mol. Compared to BP1, hydroxyl and methoxy substitutions enhanced the BPs-HSA binding. The combined effect of the number and site of hydroxyl substitution at BPs determined the binding strength between BPs and HSA. It was more accessible to bind HSA when BPs were substituted with para-hydroxyl (4-hydroxyl) groups than with ortho-hydroxyl (2-hydroxyl) groups. Moreover, the additional para-methoxy (4-methoxy) group increased the BP-HSA binding strength by approximately 47 times under the same hydroxyl substitution conditions. Theoretical calculations revealed that functional group substitutions increased the intermolecular binding force by increasing the negative electrostatic potential surface area of BPs, which significantly increased the electrostatic and dispersion forces between the BPs and HSA. This BPs-HSA binding decreased the α-helix of HSA and influenced the ratio of other secondary structures, including β-sheet, β-turn, and random coil of HSA. This study provides a theoretical and experimental foundation for understanding the human health risks associated with BPs.

One-step self-assembly of Fe-biochar composite for enhanced persulfate activation to phenol degradation: Different active sites-induced radical/non-radical mechanism

Persulfate (PS) activation by nanoscale zerovalent iron (nZVI) is promising for water purification, while is limited due to its easy agglomeration and oxidation. Herein, nZVI encapsuled in carbon matrix shell was synthesized via one-step carbothermal reduction. The core-shell structure effectively inhibited oxidation and agglomeration of nZVI core, and graphitized porous structures facilitated phenol binding with maximal adsorption capacity of 117.10 mg/g achieved by nZVI_0.6-BC₈₀₀. Both reactive oxygen species (SO₄^•-, O•H, O₂^•- and ¹O₂) and electron transfer process resulted in phenol decomposition. Owing to diversified active sites, the nZVI_0.6-BC₈₀₀/PS system could completely degrade phenol degradation within short time, and exhibited great adaptation to extensive pH range (3.0-9.0) and coexisting substances. Additionally, the nZVI_0.6-BC₈₀₀/PS system could maintain over 85% removal of phenol after three recycles or 50 days of storage, and was highly-efficient to different water environments, thus proposing rational design of iron-carbon catalyst with potential in water treatment.