Generalized two-dimensional perturbation correlation infrared spectroscopy reveals mechanisms for the development of surface charge and recalcitrance in plant-derived biochars

Properties of biochar colloids and behaviors in the soil environment: Influencing the migration of heavy metals

Biochar pyrolyzed by biomass shows excellent application prospects for heavy metal (HM) remediation, but a part of biochar can be inevitably broken into micro- and nano-sized biochar colloids (BCs) under biological and physicochemical actions in soil. BCs derived in the process of remediation have rough surface, rich elemental species and contents, and multiple functional groups, which are similar to biochar. However, BCs have some unique colloidal properties because of their micro and nano scale size. Due to these properties, BCs exhibit strong mobilities in the soil environment, and the mobilities may be influenced by a combination of colloidal properties of BCs and environmental factors including soil colloids and other soil environmental conditions. In addition, BCs may have affinity effects on HMs through electrostatic adsorption, ion exchange, surface complexation, precipitation/co-precipitation, and redox because of the properties such as large specific surface area, and rich oxygen-containing functional groups and minerals on the surface. This review summarizes the physicochemical and migratory properties of BCs, and the internal and external factors affecting the migration of BCs in the soil environment, and the possible effects of BCs on HMs are high-lighted. This review provides a theoretical basis for the optimization of soil contaminated with HMs after remediation using biochar. Notably, the innovative idea that BCs may influence the presence of HMs in soil needs to be further confirmed by more targeted detection and analysis methods in future studies to prevent the possible environmental toxicities of the lateral and vertical diffusion of HM caused by BCs in soil.

Abating ammonia emission from poultry manure by Pt/TiO2 modified corn straw

Poultry manure is a significant source of ammonia (NH3) emissions, which not only poses detrimental impacts on human well-being and the ecological system, but also leads to economic losses in the agricultural industry. Herein, we modified corn straw (CS) with 1 wt% Pt/TiO2 catalysts using a low-temperature partial-oxidation technology to mitigate NH3 emissions from poultry manure. It was found that Pt/TiO2 can enable exothermic processes to occur at lower temperatures by reducing the activation energy. Under optimal modification conditions of 220 °C, the NH3 uptakes of modified CS samples were markedly greater compared to those of the original CS. Addition of 20-50% modified CS to poultry manure resulted in significant reductions of 54.1-98.6% in NH3 emissions compared to the control. Mechanistic studies indicate that NH3 adsorption on the modified CS is mainly driven by the presence of acidic and alkaline functional groups, while surface area and pore structure have a negligible effect. XPS combined with NH3-TPD reveals that the formation of amide and amine bonds contributes to the excellent stability of adsorbed NH3. H2-TPR, O2-TPD, and d-band theory suggest that strong metal-support interactions between Pt and TiO2 could be particularly crucial in catalyzing CS modification. This study proposes an environmentally sustainable and economically viable solution for abating NH3 emissions from poultry manure, thereby addressing crucial environmental and economic concerns in the agricultural sector.

The potential of biochar as a microbial carrier for agricultural and environmental applications

Biochar can be an effective carrier for microbial inoculants because of its favourable properties promoting microbial life. In this review, we assess the effectiveness of biochar as a microbial carrier for agricultural and environmental applications. Biochar is enriched with organic carbon, contains nitrogen, phosphorus, and potassium as nutrients, and has a high porosity and moisture-holding capacity. The large number of active hydroxyl, carboxyl, sulfonic acid group, amino, imino, and acylamino hydroxyl and carboxyl functional groups are effective for microbial cell adhesion and proliferation. The use of biochar as a carrier of microbial inoculum has been shown to enhance the persistence, survival and colonization of inoculated microbes in soil and plant roots, which play a crucial role in soil biochemical processes, nutrient and carbon cycling, and soil contamination remediation. Moreover, biochar-based microbial inoculants including probiotics effectively promote plant growth and remediate soil contaminated with organic pollutants. These findings suggest that biochar can serve as a promising substitute for non-renewable substrates, such as peat, to formulate and deliver microbial inoculants. The future research directions in relation to improving the carrier material performance and expanding the potential applications of this emerging biochar-based microbial immobilization technology have been proposed.

In-depth insight into the effects of intrinsic calcium compounds on the pyrolysis of hazardous petrochemical sludge

To understand the potential effects of intrinsic calcium compounds on sludge pyrolysis, the pyrolysis behavior of petrochemical sludge (PS), calcium carbonate blend PS (CaPS), and decalcified PS (DePS) were investigated using thermogravimetric analysis (TGA) and in-situ Fourier-transform infrared spectroscopy coupled with pyrolysis-gas chromatography and mass spectrometry (Py-GC/MS). The TGA results indicated that decalcification increased and decreased the energy barriers of PS decomposition in ranges 200-350 °C and 350-600 °C, respectively. In contrast, copyrolysis with CaCO₃ decreased the activation energy (E) of the pseudoreaction phase 2 (PH2) and altered the mechanism model. Meanwhile, during copyrolysis, char deposition and interaction hindered CaCO₃ decomposition. The two-dimensional correlation spectroscopy results, on the other hand, showed that the reaction priority of O-containing groups and CH- vibration of methyl groups were affected by both decalcification and CaCO₃ copyrolysis. The Py-GC/MS results indicated that the three sludges mainly released hydrocarbons, N-containing organics, alcohols, aldehydes, and acids. During pyrolysis, CaCO₃ also played a neutralization role, which reduced the release of pyrolytic acidic products. In addition, the increase of the pyrolysis temperature increased the hydrocarbon content. This research will guide the industrial application of sludge pyrolysis.

Customized oxygen-rich biochar with ultrahigh microporosity for ideal solid phase microextraction of substituted benzenes

The synergistic effect of high microporosity and abundant heteroatoms is important for improving the performance of biochar in various fields. However, it is still challenging to create enough micropores for biochar, while simultaneously retaining the heteroatoms from biomass. A series of biochar with variable microstructures was successfully prepared by carbonization and following ball milling on lotus pedicel (LP), watermelon rind (WR), and litchi rind (LR). The pore structures and heteroatoms of biochar were characterized in detail. Notably, high microporosity could be realized by the carbonization of LR, and further ball milling resulted in a higher microporous surface area (1323.4 m²·g^-1) and richer oxygen. Furthermore, the obtained biochar was fabricated as solid phase microextraction (SPME) coatings with uniform morphologies and similar thicknesses to deeply investigate the relationships between the microstructures and extraction performance. The best performance was demonstrated by the LR800BM, with enrichment factors from 1780 to 155,217. Finally, it was coupled with gas chromatography-mass spectrometry (GC-MS) to develop an analytical method with a wide linear range (1-50,000 ng·L^-1), low limits of detection (0.10-1.4 ng·L^-1), good repeatability (0.83 %-7.5 %) and reproducibility (4.2 %-8.9 %). This work provides valuable insights into the structure-performance relationship of biochar, which is important for the design of high-performance biochar-based adsorbents and their applications in the environment.

Effect of combined aging treatment on biochar adsorption and speciation distribution for Cd(II)

As a passivation material for heavy metals in-situ remediation, biochar (BC) has often been expected to maintain long-term adsorption performance for target pollutants. There is still lack of consensus about the impact of aging processes on biochar properties, particularly with respect to its long-term sorption performance. In this study, the changes to immobilization mechanisms as well as the speciation distribution of Cd(II) triggered by combined aging simulation (dry-wet, freeze-thaw cycle and oxidation treatment) on BC prepared under three levels of pyrolysis temperatures (300, 500 and 700 °C) were investigated. The results showed significant inhibition of aging on adsorption performance with the adsorptive capacity of BC300, BC500 and BC700 for Cd(II) decreased by 31.12 %, 50.63 % and 14.94 %, respectively. However, sequential extraction results indicated little influence of the aging process on the relative fractionation of Cd(II) speciation. The distribution of readily bioavailable, potentially bioavailable and non-bioavailable fractions of Cd(II) on BC showed only minimal changes post-aging. Overall, there was less Cd(II) sorption following aging, but the fractional availability (in relative terms) remained the same. Compared with 300 and 700 °C, the biochar prepared under 500 °C accounted the highest fraction of non-bioavailable Cd(II) (67.23 % of BC500, 59.17 % of Aged-500), and thus showed most promising for Cd(II) immobilization. This study has important practical significance for the long-term application of biochar in real environment.

Catalytic modification of corn straw facilitates the remediation of Cd contaminated water and soil

Turning postharvest residue into high-value-added products is crucial for agricultural waste management and environmental remediation. In this proof-of-concept study, nanosized Pt/TiO₂ was used as a model catalyst to modify corn straw (CS) materials through a simple low-temperature oxidation process. This method was demonstrated to be self-sustainable, waste-free, and with high yields. At an optimal temperature of 220 °C, O₂ treatment with 1 wt% Pt/TiO₂ greatly changed ultra-micropore and mesopore structures, dissolved organic carbon, aromatic contents and surface oxygen (O)-containing functional groups in CS products. This treatment resulted in an approximately 5-fold increase of cadmium (Cd) adsorption from aqueous solution and immobilization rate of 43.1% at 7d for bioavailable Cd in soil. Spectroscopic and linear regression analysis demonstrated that both acidic and basic functional groups in CS contributed to Cd adsorption, suggesting chemical adsorption. According to the d-band theory, the unexpected role of catalysts in CS modification could be associated with dissociative adsorption of molecular O₂ on the Pt surface. These results provide insights for the development of economic and sustainable technologies to reutilize agricultural waste biomass for water and soil remediation.

Formation of emerging disinfection byproducts from agricultural biomass-derived DOM: Overlooked health risk source

Carbon-derived dissolved organic matter (CDOM) are inevitably released to surface water during returning agricultural biomass carbon to farmland, which are potential precursors of disinfection byproducts (DBPs). In this study, CDOM was extracted from aerobic incineration ("OX") and anoxic pyrolysis ("PY") of three kinds of straw (wheat, corn, and rice), and the emerging DBPs from them were deciphered. The CDOM with molecular weight < 1 kDa in the OX and PY groups accounted for 53-87%, and it was higher in the PY group. A total 1343-2107 of CHO and 641-1761 of CHNO formulas were detected in the CDOM derived from the OX group, among which 74%-83% contained aromatic structures rich in oxygen containing groups. 1919-3289 of CHO and 785-1954 of CHNO formulas were observed in the PY group, and 77%-86% of them were lignins/CRAM-like compounds. Surprisingly, 765-2158 and 895-1648 of emerging DBPs were identified in the OX and PY groups, and the proportions of N-DBPs were 20.3-54.8% and 2.8-4.8%, respectively. Based on HOCl addition and Cl substitution mechanisms, the H/C ratios of the DBP precursors in the OX and PY groups were in the range of 0.2-1.5 and 0.6-2.0, respectively. The DBPs derived from the OX group exhibited higher cytotoxicity and genotoxicity due to the higher aromaticity and more N-DBPs. Thus, returning agricultural biomass carbon, particularly that produced by direct combustion, to farmland brought potential threat to drinking water safety.

Continuing progress in the field of two-dimensional correlation spectroscopy (2D-COS), part II. Recent noteworthy developments

This comprehensive survey review compiles noteworthy developments and new concepts of two-dimensional correlation spectroscopy (2D-COS) for the last two years. It covers review articles, books, proceedings, and numerous research papers published on 2D-COS, as well as patent and publication trends. 2D-COS continues to evolve and grow with new significant developments and versatile applications in diverse scientific fields. The healthy, vigorous, and diverse progress of 2D-COS studies in many fields strongly confirms that it is well accepted as a powerful analytical technique to provide an in-depth understanding of systems of interest.

A critical review on biochar-assisted free radicals mediated redox reactions influencing transformation of potentially toxic metals: Occurrence, formation, and environmental applications

Potentially toxic metals have become a viable threat to the ecosystem due to their carcinogenic nature. Biochar has gained substantial interest due to its redox-mediated processes and redox-active metals. Biochar has the capacity to directly adsorb the pollutants from contaminated environments through several mechanisms such as coprecipitation, complexation, ion exchange, and electrostatic interaction. Biochar's electron-mediating potential may be influenced by the cyclic transition of surface moieties and conjugated carbon structures. Thus, pyrolysis configuration, biomass material, retention time, oxygen flow, and heating time also affect biochar's redox properties. Generally, reactive oxygen species (ROS) exist as free radicals (FRs) in radical and non-radical forms, i.e., hydroxyl radical, superoxide, nitric oxide, hydrogen peroxide, and singlet oxygen. Heavy metals are involved in the production of FRs during redox-mediated reactions, which may contribute to ROS formation. This review aims to critically evaluate the redox-mediated characteristics of biochar produced from various biomass feedstocks under different pyrolysis conditions. In addition, we assessed the impact of biochar-assisted FRs redox-mediated processes on heavy metal immobilization and mobility. We also revealed new insights into the function of FRs in biochar and its potential uses for environment-friendly remediation and reducing the dependency on fossil-based materials, utilizing local residual biomass as a raw material in terms of sustainability.

Continuing progress in the field of two-dimensional correlation spectroscopy (2D-COS), part I. Yesterday and today

This comprehensive survey review, as the first of three parts, compiles past developments and early concepts of two-dimensional correlation spectroscopy (2D-COS) and subsequent evolution, as well as its early applications in various fields for the last 35 years. It covers past review articles, books, proceedings, and numerous research papers published on 2D-COS. 2D-COS continues to evolve and grow with new significant developments and versatile applications in diverse scientific fields. The healthy, vigorous, and diverse progress of 2D-COS studies in many fields confirms that it is well accepted as a powerful analytical technique to provide the in-depth understanding of systems of interest.

Fast pyrolysis of guaiacyl-syringyl (GS) type milled wood lignin: Product characteristics and CH4 formation mechanism study

It is anticipated that the insight into the demethylation and mechanism of CH₄ formation from natural lignin using in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ FTIR) combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) and density functional theory (DFT) calculation analysis would contribute to a deeper insight of bond cleavage mechanism of lignin pyrolysis. Herein, GS-type lignin (poplar MWL) was characterized by Fourier transform infrared spectroscopy (FTIR) and heteronuclear Single-Quantum Correlation Nuclear Magnetic Resonance (HSQC), and its pyrolysis at different temperatures was performed in a lab-scale fixed-bed reactor. The biochar, gaseous and liquid products were qualitative, and quantitative analysis of gases and bio-oil is demonstrated using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The key of CH₄ formation is the homolytic cleavage of the methoxyl functional group generating methyl radical and further verified via in-situ FTIR combined with 2D-PCIS and DFT calculation. The study established a new methodology based on multiple factor analysis to evaluate the CH₄ formation mechanism in GS-type milled wood lignin at the molecular level, which is of positive significance for increasing lignin valorization and improving the environment.

Spectral characteristics of dissolved organic carbon (DOC) derived from biomass pyrolysis: Biochar-derived DOC versus smoke-derived DOC, and their differences from natural DOC

Biochar-derived dissolved organic carbon (BDOC) and smoke-derived dissolved organic carbon (SDOC) are two different biomass-pyrogenic DOCs. They inevitably enter soil and water, then potentially pose different impacts on the chemistry of these media. This study systemically investigated the emissions and spectral characteristics of BDOC and SDOC as well as their differences from natural DOC. The results showed that the emission of SDOC was 1-3 orders of magnitude greater than that of BDOC after biomass pyrolysis. UV-vis spectra indicated that BDOC had higher aromaticity and molecular weight as well as lower polarity than SDOC. The two-dimensional correlation infrared spectrum (2D-PCIS) matrix indicated that BDOC contained more chemical groups with stronger temperature-dependence than SDOC. Fluorescence EEM-PARAFAC analysis showed that BDOC was dominated by macromolecular humic-like substances, while SDOC was primarily composed of small molecules of aromatic protein/polyphenols-like compounds. The fluorescence indicators including humification index (HIX) (0.08-0.76) and biological index (BIX) (1.18-1.72) of SDOC were significantly different from those of BDOC (HIX: 1.64-12.68, and BIX: 0.17-1.62). The higher BIX and more small molecules of aromatic protein/polyphenols-like compounds indicated SDOC had potentially higher bioavailability and turnover rate in the environment than BDOC. Furthermore, the UV-vis spectral indicator (S_275-295) and fluorescence spectral indicators (HIX, and BIX) of BDOC were equivalent to those of natural DOC, whereas these indicators of SDOC were significantly different from those of natural DOC. This study demonstrated that BDOC and SDOC had significantly different components and properties and they might present different environmental behaviors and effects.

Investigating Biochar-Derived Dissolved Organic Carbon (DOC) Components Extracted Using a Sequential Extraction Protocol

Biochar-derived dissolved organic carbon (DOC), as the most important component of biochar, can be released on farmland, improving fertility and playing a role in soil amendment and remediation. The complexity of molecular structures and diversity of DOC compounds have influenced these functions to some extent. A sequential extract protocol consisting of water (25 °C), hot water (80 °C), and NaOH solution (0.05 M) was used to fully extract DOC compounds and gain a thorough understanding of the possible DOC components released from biochar. Rape straw (RS), apple tree branches (ATB), and pine sawdust (PS) were pyrolyzed at 300, 500, and 700 °C, respectively, to make nine distinct biochars. A TOC analyser, ultraviolet-visible spectroscopy (UV–vis), and excitation–emission fluorescence (EEM) spectrophotometer were used in conjunction with parallel factor analysis (PARAFAC) to determine the distribution of DOC content, the diversity of aromaticity, molecular weight characteristics and components of biochar-derived DOC. The results show that the relative distribution of water-extractable fractions ranged from 3.21 to 35.57%, with a low-aromaticity and extremely hydrophilic fulvic-acid-like compounds being found in the highest amounts (C2 and C3). The smallest amount of hot water-extractable components was produced from the release of small-molecule aliphatic compounds adsorbed on biochar and susceptible to migration loss once in a soil solution. More than half of the biochar-derived DOC was released in a NaOH solution, which primarily consisted of humic-acid-like compounds (C1), with higher molecular weights, more aromaticity, and lower bioavailability, according to the distribution of DOC in various extractants. In addition, the pyrolysis temperature and biomass type had a significant impact on the DOC properties released by biochar. As a result, the findings of this study showed that using a sequential extract protocol of water, hot water, and NaOH solution in combination with spectroscopic methods could successfully reveal the diversity of biochar-derived components, which could lead to new insights for the accurate assessment of potential environmental impacts and new directions for biochar applications.

Comprehensive Estimation of Combustion Behavior and Thermochemical Structure Evolution of Four Typical Industrial Polymeric Wastes

A huge amount of industrial waste will be generated during the industrialization process and their harmless disposal has always been a headache for reducing carbon emissions. In this study, the combustion behaviors and thermal kinetics of four typical industrial polymeric wastes including rubber, leather, plastic and cloth, were systematically studied by using a Thermogravimetric Analysis. The gas emission and structural evolution was comprehensively analyzed using TG-FTIR, 2D-PCIS, ICP and TEM. The results show that the combustibility of leather and cloth are better than the other two samples, while the rubber and plastic have a wider combustion temperature range for higher content of C-H bonds and, the intermediate oxidation process and the stubborn cracking process of C=C bonds. The surface reaction was considered to be the main reaction of rubber and plastic (pre-exponential factor less than 10−9), while both leather and cloth went through a complex procedure during multiple decomposition. The volatiles products are gases (e.g., CO2, CH4) and small molecules (e.g., H2O). The high levels of basic metals in the industrial waste causes serious slagging and fouling tendency (fouling index higher than 4.0), which have a serious adverse influence on the operation of a waste incineration plant.

Overcoming biochar limitations to remediate pentachlorophenol in soil by modifying its electrochemical properties

In this study, we produced modified biochars with enhanced electrochemical properties to increase PCP remediation in soil. Although all biochars enhanced PCP remediation in aerobic conditions, only a few did in anaerobic soil. The most successful modifications were (i) the preloading of biomass with 10% w/w FeCl₃, to obtain a biochar rich in redox-active metals (B-Fe); (ii) the oxidation of a conductive biochar pyrolyzed at 1000 ºC with 0.025 M KMnO₄, to produce a biochar with both moderate conductivity and redox capacity (B-1000-KMnO₄); and (iii) KMnO₄ oxidation of an amorphous biochar pyrolyzed at 400 ºC to obtain a biochar with very high redox capacity (B-KMnO₄). B-Fe reduced extractable PCP to almost zero after 50 days in both incubations, but showed slow kinetics of remediation in aerobic soil. B-1000-KMnO₄ had the highest rate of remediation under aerobic conditions, but no significant effect under anaerobic conditions. B-KMnO₄, however, presented high rates of remediation and high removal of extractable PCP under both conditions, which made it the recommended modification strategy for increased PCP remediation. We found that the degree of remediation primarily depends on the redox capacity, while the rate of remediation was determined by both the conductivity and redox capacity of biochar.

Characterization of Biochar Derived from Crop Residues for Soil Amendment, Carbon Sequestration and Energy Use

The crop residues generated in agricultural fields are mostly considered a burden due to their disposal issues. This study attempts to effectively use pigeon pea stalk (PPS) for biochar production, a promising source as a soil amendment for carbon sequestration and alternative fuel source. PPS was pyrolyzed at different loads and reaction times to optimize the kiln temperature (350–400 °C and 450–500 °C) and changes in physicochemical properties, higher heating value (HHV) and yield were assessed. The results indicated that biochar yield, volatile matter, bulk density, O/C and H/C atomic ratios decreased, whereas fixed carbon, ash content and total porosity increased with increasing kiln temperature across all loads. Biochar produced at 450–500 °C (18 kg load kiln−1) had higher total carbon, nitrogen, phosphorous, recovered total carbon and total nitrogen, total potential carbon and CO2 reduction potential. Biochar produced at 350–400 °C had the maximum cation exchange capability (43.0 cmol kg−1). Biochar has estimated O/C and H/C atomic ratios of 0.07–0.15 and 0.35–0.50, respectively. Biochar exhibited good agronomic characteristics and fulfilled key quality criteria of H/C < 0.7 and O/C < 0.4 for soil carbon sequestration, as described by the European Biochar Certificate and the International Biochar Initiative. The estimated mean residence time and the mass fraction of carbon that would remain after 100 years were consistently greater than 1000 years and 80%, respectively. The biochar produced at 450–500 °C (at 18.0 kg kiln−1) from PPS had higher fixed carbon (65.3%), energy density (1.51), energetic retention efficiency (53%), fuel ratio (4.88), and HHV (25.01 MJ kg−1), as well as lower H/C and O/C ratios, implying that it is suitable for use as an alternative solid fuel.

Biochar - An effective additive for improving quality and reducing ecological risk of compost: A global meta-analysis

Biochar is considered as a promising additive with multi-benefits to compost production. However, how the biochar properties and composting conditions affect the composting process and quality and ecological risk of compost is still unclear. In the present study, we conducted a global meta-analysis based on 876 observations from 84 studies. Overall, regardless of biochar properties and composting conditions, biochar addition could significantly increase the pH (5.90%), germination index (26.6%), contents of nitrate nitrogen (56.6%), total nitrogen (9.50%), and total potassium (10.1%), and degree of polymerization (29.4%) while decrease the electrical conductivity (-5.70%), contents of ammonium nitrogen (-33.7%), bioavailable zinc (-22.9%), and bioavailable copper (-38.6%), and emissions of ammonia (-44.2%), nitrous oxide (-68.4%), and methane (-61.7%). Other compost indicators, including the carbon to nitrogen ratio and total phosphorus content, were found to be insignificantly affected by biochar addition. The responses of tested compost indicators affected by the biochar properties and composting conditions were further explored, based on which the addition of straw biochars at a rate of 10-15% was recommended due to its greater potential to improve quality of compost and reduce its ecological risk. Combining the results of linear regression analysis and structural equation model, the increase in compost pH caused by biochar addition was identified as the key mechanism for the increased nutrient content and decreased heavy metal bioavailability. These results could guide us to choose suitable kinds of biochar or develop engineered biochars with specific functionality to realize an optimal compost production mode.

Green synthesis of magnetically recyclable Mn0.6Zn0.4Fe2O4@Zn1-xMnxS composites from spent batteries for visible light photocatalytic degradation of phenol

Magnetic binary heterojunctions are a kind of promising photocatalysts due to their high catalytic activity and easy magnetic separation; however, their synthesis may involve high costs or secondary environmental impacts. In this work, the magnetically recyclable Mn_0.6Zn_0.4Fe₂O₄@Zn_1-xMn_xS (MZFO@Zn_1-xMn_xS, x = 0.00-0.07) photocatalysts are synthesized from spent batteries via a green biocheaching and egg white-assisted hydrothermal method. The as-synthesized photocatalysts have been comprehensively characterized in phase, morphology, texture, optics, photoelectrochemistry and photocatalytic activity. Characterization results indicate that the desired core-shell structure MZFO@Zn_1-xMn_xS composites are successfully synthesized, theirs absorption intensity in the visible light region is greatly enhanced compared to Zn_1-xMn_xS. In addition, doped Mn²⁺ in ZnS host lattice and the staggered bandgap alignment of MZFO and Zn_1-xMn_xS greatly enhances electron transfer and charge separation in the binary heterojunction system. The optimized MZFO@Zn_0.95Mn_0.05S shows the highest photodegradation performance toward phenol under the visible light irradiation, with a complete degradation of 25 mg L^-1 of phenol within 120 min, and its reactive kinetic constants is about 5.2 and 13.3 times higher than that of pure Zn_0.95Mn_0.05S and MZFO, respectively. Furthermore, the mechanism and pathways for the degradation of phenol are proposed. In addition, MZFO@Zn_0.95Mn_0.05S also exhibits a good reusability and high magnetic separation properties after 5 successive cycles. This new material has the advantages of low costs, simple reuse and great potential in application.

Stimulation of pyrolytic carbon materials as electron shuttles on the anaerobic transformation of recalcitrant organic pollutants: A review

Pyrolytic carbon materials (PCMs) with various surface functionalities are widely used as environmentally friendly and cost-efficient adsorbents for the removal of organic and inorganic pollutants. Recent studies have illustrated that PCMs as electron shuttles (ESs) could also show excellent performances in promoting the anaerobic transformation of recalcitrant organic pollutants (ROPs). Numerous studies have demonstrated the excellent electron-shuttle capability (ESC) of PCMs to stimulate the anaerobic reductive transformation of ROPs. However, there is a lack of consistent understanding of the mechanism of ESC formation in PCMs and the stimulation mechanism for ROPs anaerobic transformation. To gain a more comprehensive understanding of the latest developments in the study of PCMs as ESs for ROPs anaerobic transformation, this review summarizes the formation mechanism, influencing factors, and stimulation mechanisms of ESC. ESC benefits from redox functional groups (quinone and phenol groups), persistent free radicals (PFRs), redox-active metal ions, conductive graphene phase, and porous nature of their surface. The factors influencing ESC include the highest treatment temperature (HTT), feedstocks, modification methods, and environmental conditions, of which, the HTT is the key factor. PCMs promote the reductive transformation of ROPs under anaerobic conditions via abiotic and biotic pathways. Eventually, the prospects for the ROPs anaerobic transformation enhanced by PCMs are proposed.

Tuning oxygenated functional groups on biochar for water pollution control: A critical review

Biochar has attracted increasing attention in water pollution control, attributed to its various merits, e.g., tunable physico-chemical properties. The oxygenated functional groups (OFGs) on biochar are key active sites for removing pollutants from water through interfacial adsorption/redox reaction. However, there is still a lack of comprehensive knowledge and perspective on tuning OFGs on biochar for enhanced performance in water pollution control. Here, this review highlighted the mechanisms of biochar OFGs in water pollution control, analyzed the strategies and mechanisms for tuning OFGs on biochar, and investigated the performances of biochars with tuned OFGs in removing inorganic/organic pollutants via adsorption/redox reactions. Specifically, strategies for tuning OFGs on biochar are far more than the well-recognized ex-situ oxidation of pristine biochar. These strategies include in-situ low temperature preservation of hydroxyl and carboxyl, in-/ex-situ oxidation of biochar, and in-/ex-situ grafting of carboxyl on biochar via cycloaddition/acylation reaction. The resultant biochars showed enhanced performances in adsorption (mainly mediated by hydroxyl, carboxyl and ketone through surface complexation, H-bonding, and electrostatic attraction) and redox reaction (mainly mediated by redox-active hydroxyl and ketone). Finally, this review presented future directions on developing biochar with specially tuned surface OFGs as a sustainable high-performance adsorbent/carbocatalyst for water pollution control.

Pyrolysis temperature-dependent carbon retention and stability of biochar with participation of calcium: Implications to carbon sequestration

Converting biomass waste into biochar by slow pyrolysis with subsequent soil amendment is a prospective approach with multiple environmental benefits including soil contamination remediation, soil amelioration and carbon sequestration. This study selected cow manure as precursor to produce biochar under 300 °C, 400 °C, 500 °C and 600 °C, and a remarkable promotion of carbon (C) retention in biochar by incorporation of exogenous Ca was achieved at all investigated pyrolysis temperatures. The C retention was elevated from 49.2 to 68.3% of pristine biochars to 66.1-79.7% of Ca-composite biochars. It was interesting that extent of this improvement increased gradually with rising of pyrolysis temperature, i.e., doping Ca in biomass promoted pyrolytic C retention in biochar by 16.6%, 23.4%, 29.1% and 31.1% for 300 °C, 400 °C, 500 °C and 600 °C, respectively. Thermogravimetric-mass spectrometer (TG-MS) and X-ray photoelectron spectroscopy (XPS) showed that Ca catalyzed thermal-chemical reactions and simultaneously suppressed the release of small organic molecular substances (C₂-C₇) via physical blocking (CaO, CaCO₃, and CaClOH) and chemical bonding (CO and OC-O). The catalyzation mainly occurred at 200-400 °C, while the suppression was more prominent at higher temperatures. Raman spectra and 2D FTIR analysis on biochar microstructure showed that presence of Ca had negative influence on carbon aromatization and thus weakened biochar's stability, while increasing pyrolysis temperature enhanced the stability of carbon structure. Finally, with integrating "C retention" during pyrolysis and "C stability" in biochar, the maximum C sequestration (56.3%) was achieved at 600 °C with the participation of Ca. The study highlights the importance of both Ca and pyrolysis temperature in enhancing biochar's capacity of sequestrating C.

Hydrochar derived from municipal sludge through hydrothermal processing: A critical review on its formation, characterization, and valorization

Additional options for the sustainable treatment of municipal sludge are required due to the significant amounts of sludge, high levels of nutrients (e.g., C, N, and P), and trace constituents it contains. Hydrothermal processing of municipal sludge has recently been recognized as a promising technology to efficiently reduce waste volume, recover bioenergy, destroy organic contaminants, and eliminate pathogens. However, a considerable amount of solid residue, called hydrochar, could remain after hydrothermal treatment. This hydrochar can contain abundant amounts of energy (with a higher heating value up to 24 MJ/kg, dry basis), nutrients, and trace elements, as well as surface functional groups. The valorization of sludge-derived hydrochar can facilitate the development and application of hydrothermal technologies. This review summarizes the formation pathways from municipal sludge to hydrochar, specifically, the impact of hydrothermal conditions on reaction mechanisms and product distribution. Moreover, this study comprehensively encapsulates the described characteristics of hydrochar produced under a wide range of conditions: Yield, energy density, physicochemical properties, elemental distribution, contaminants of concern, surface functionality, and morphology. More importantly, this review compares and evaluates the current state of applications of hydrochar: Energy production, agricultural application, adsorption, heterogeneous catalysis, and nutrient recovery. Ultimately, along with the identified challenges and prospects of valorization approaches for sludge-derived hydrochar, conceptual designs of sustainable municipal sludge management are proposed.

Trace metal elements mediated co-pyrolysis of biomass and bentonite for the synthesis of biochar with high stability

The stability of biochar is a crucial parameter in determining the potential of biochar for carbon sequestration. Many studies have demonstrated that the addition of clay during the pyrolysis of biomass is beneficial for the production of biochar with a high stability, but finding a strategy for a further improvement of stability of clay-modified biochar is still highly desirable. Herein, the co-pyrolysis of biomass and clay mediated by trace metal elements is proposed as a new strategy for the production of biochar with exceptionally high stability. The results indicate that the biochar resistance index for biochar obtained from the trace metal elements mediated the co-pyrolysis of biomass and clay is ~0.75, which is much higher than that of biochars obtained from biomass pyrolysis or the co-pyrolysis of biomass and clay, demonstrating that the presence of metal ions during the co-pyrolytic process can significantly improve the oxidation resistance of biochar. Thermogravimetric analysis reveals that the carbon retention value is reduced when the addition of metal ions during the co-pyrolytic process, and the presence of metal ions can reduce the starting temperature of the pyrolysis reaction and catalyze the process of biomass pyrolysis. In addition, the percentages of CC, CC, and CH in all biochars obtained from trace metal elements mediated the co-pyrolysis of biomass and clay are greater than 41.82%, which are higher than that of original biochar. Besides, the percentage of oxygen-containing functional groups is found to be decreased after the presence of metal ions during the co-pyrolytic process. The presence of metal ions can form metal nano-sulfides and oxides on the surface, which plays a physical barrier to the anti-oxidation performance of biochar. Furthermore, compared to BBC or BC, MnBBC and ZnBBC have a better leaching resistance to P, while FeBBC has almost no leaching resistance to soil P. Overall, the study reveals that the addition of trace element metal ions during the co-prolysis of biomass and bentonite is an effective method to increase the stability of obtained biochar, and it is also beneficial for retarding the release of nutrients in the soil and thus increase the utilization of nutrients.

Application of biochars in the remediation of chromium contamination: Fabrication, mechanisms, and interfering species

Chromium (Cr) is one of the most toxic pollutants that has accumulated in terrestrial and aqueous systems, posing serious risks towards living beings on a worldwide scale. The immobilization, removal, and detoxification of active Cr from natural environment can be accomplished using multiple advanced materials. Biochar, a carbonaceous pyrolytic product made from biomass waste, is considered as a promising material for the elimination of Cr contamination. The preparation and properties of biochar as well as its remediation process for Cr ions have been well investigated. However, the distinct correlation of the manufacturing, characteristics, and mechanisms involved in the remediation of Cr contamination by various designed biochars is not summarized. Herein, this review provides information about the production, modification, and characteristics of biochars along with their corresponding effects on Cr stabilization. Biochar could be modified via physical, hybrid, chemical, and biological methods. The remediating mechanisms of Cr contamination using biochars involve adsorption, reduction, electron shuttle, and photocatalysis. Moreover, the coexisting ions and organic pollutants change the pattern of the remediating process of biochar in actual Cr contaminated water and soil. Finally, the present limitations and future perspectives are proposed.

Co-application of biochar and nitrogen fertilizer reduced nitrogen losses from soil

Combined application of biochar and nitrogen (N) fertilizer has the potential to reduce N losses from soil. However, the effectiveness of biochar amendment on N management can vary with biochar types with different physical and chemical properties. This study aimed to assess the effect of two types of hardwood biochar with different ash contents and cation exchange capacity (CEC) on soil N mineralization and nitrous oxide (N2O) production when applied alone and in combination with N fertilizer. Soil samples collected from a temperate pasture system were amended with two types of biochar (B1 and B2), urea, and urea plus biochar, and incubated for 60 days along with soil control (without biochar or urea addition). Soil nitrate N, ammonium N, ammonia-oxidizing bacteria amoA gene transcripts, and N2O production were measured during the experiment. Compared to control, addition of B1 (higher CEC and lower ash content) alone decreased nitrate N concentration by 21% to 45% during the incubation period while the addition of B2 (lower CEC and higher ash content) alone increased the nitrate N concentration during the first 10 days. Biochar B1 also reduced the abundance of amoA transcripts by 71% after 60 days. Compared to B1 + urea, B2 + urea resulted in a significantly greater initial increase in soil ammonium and nitrate N concentrations. However, B2 + urea had a significantly lower 60-day cumulative N2O emission compared to B1 + urea. Overall, when applied with urea, the biochar with higher CEC reduced ammonification and nitrification rates, while biochar with higher ash content reduced N N2O production. Our study demonstrated that biochar has the potential to enhance N retention in soil and reduce N2O emission when it is applied with urea, but the specific effects of the added biochar depend on its physical and chemical properties.

Fresh biochar application provokes a reduction of nitrate which is unexplained by conventional mechanisms

Soil-applied biochar has been reported to possess the potential to mitigate nitrate leaching and thus, exert beneficial effects beyond carbon sequestration. The main objective of the present study is to confirm if a pine gasification biochar that has proven able to decrease soil-soluble nitrate in previous research can indeed exert such an effect and to determine by which mechanism. For this purpose, lysimeters containing soil-biochar mixtures at 0, 12 and 50 t biochar ha^-1 were investigated in two different scenarios: a fresh biochar scenario consisting of fresh biochar and a fallow-managed soil, and an aged biochar scenario with a 6-yr naturally aged biochar in a crop-managed soil. Soil columns were assessed under a mimicked Mediterranean ambient within a greenhouse setting during an 8-mo period which included a barley crop cycle. A set of parameters related to nitrogen cycling, and particularly to mechanisms that could directly or indirectly explain nitrate content reduction (i.e., sorption, leaching, microbially-mediated processes, volatilisation, plant uptake, and ecotoxicological effects), were assessed. Specific measurements included soil solution and leachate ionic composition, microbial biomass and activity, greenhouse gas (GHG) emissions, N and O isotopic composition of nitrate, crop yield and quality, and ecotoxicological endpoints, among others. Nitrate content reduction in soil solution was verified for the fresh biochar scenario in both 12 and 50 t ha^-1 treatments and was coupled to a significant reduction of chloride, sodium, calcium and magnesium. This effect was noticed only after eight months of biochar application thus suggesting a time-dependent process. All other mechanisms tested being discarded, the formation of an organo-mineral coating emerges as a plausible explanation for the ionic content decrease.

Assessment of Bioavailability of Biochar-Sorbed Tetracycline to Escherichia coli for Activation of Antibiotic Resistance Genes

Human overuse and misuse of antibiotics have caused the wide dissemination of antibiotics in the environment, which has promoted the development and proliferation of antibiotic resistance genes (ARGs) in soils. Biochar (BC) with strong sorption affinity to many antibiotics is considered to sequester antibiotics and hence mitigate their impacts to bacterial communities in soils. However, little is known about whether BC-sorbed antibiotics are bioavailable and exert selective pressure on soil bacteria. In this study, we probed the bioavailability of tetracycline sorbed by BCs prepared from rice-, wheat-, maize-, and bean-straw feedstock using Escherichia coli MC4100/pTGM bioreporter strain. The results revealed that BC-sorbed tetracycline was still bioavailable to the E. coli attached to BC surfaces. Tetracycline sorbed by BCs prepared at 400 °C (BC400) demonstrated a higher bioavailability to bacteria compared to that sorbed by BCs prepared at 500 °C (BC500). Tetracycline could be sorbed primarily in the small pores of BC500 where bacteria could not access due to the size exclusion to bacteria. In contrast, tetracycline could be sorbed mainly on BC400 surfaces where bacteria could conveniently access tetracycline. Increasing the ambient humidity apparently enhanced the bioavailability of BC400-sorbed tetracycline. BC500-sorbed tetracycline exposed to varying levels of ambient humidity showed no significant changes in bioavailability, indicating that water could not effectively mobilize tetracycline from BC500 pores to surfaces where bacteria could access tetracycline. The results from this study suggest that BCs prepared at a higher pyrolysis temperature could be more effective to sequester tetracycline and mitigate the selective pressure on soil bacteria.

Biochar as electron donor for reduction of N2O by Paracoccus denitrificans

Biochar (BC) has been shown to influence microbial denitrification and mitigate soil N2O emissions. However, it is unclear if BC is able to directly stimulate the microbial reduction of N2O to N2. We hypothesized that the ability of BC to lower N2O emissions could be related not only to its ability to store electrons, but to donate them to bacteria that enzymatically reduce N2O. Therefore, we carried out anoxic incubations with Paracoccus denitrificans, known amounts of N2O, and nine contrasting BCs, in the absence of any other electron donor or acceptor. We found a strong and direct correlation between the extent and rates of N2O reduction with BC's EDC/EEC (electron donating capacity/electron exchange capacity). Apart from the redox capacity, other BC properties were found to regulate the BC's ability to increase N2O reduction by P. denitrificans. For this specific BC series, we found that a high H/C and ash content, low surface area and poor lignin feedstocks favored N2O reduction. This provides valuable information for producing tailored BCs with the potential to assist and promote the reduction of N2O in the pursuit of reducing this greenhouse gas emissions.

Hydochar and biochar: Production, physicochemical properties and techno-economic analysis

Utilization of natural, abundant, and renewable resources for the production of carbon materials with simple and energy-efficient processes is an upsurge interest. The production processes and resultant biochar can address widespread concerns such as climate change, energy crisis, and environmental pollution. The properties of produced chars (biochar/hydrochar) depend on the production methods, feedstock, and operating parameters, which significantly affect their use for various applications. In this review, production, physiochemical properties, and techno-economic analysis of chars are summarized. This review provides the fundamentals and reaction mechanism of char production methodologies. Physicochemical properties based on chemical composition, functional groups, structure, porosity, and shapes have been compared. The effects of operating parameters on the physicochemical properties of chars are discussed. In addition, this review offers insights on new directions for char production and research in the future, based on the updated and detailed investigation of energy balance with economy of char production methodologies.

Green synthesis of a novel Mn-Zn ferrite/biochar composite from waste batteries and pine sawdust for Pb2+ removal

Magnetic ferrite/biochar composites are a kind of promising adsorbents due to their high adsorption efficiency and facile magnetic separation; however, their synthesis is associated with high cost and secondary environmental impacts. In this study, a novel Mn-Zn ferrite/biochar composite (MZF-BC) is synthesized via a green two-step biocheaching and hydrothermal method using waste batteries and pine sawdust. Characterization results indicate that the introduced Mn-Zn ferrite particles are successfully embedded and coated on biochar (BC), and synthesized MZF-BC₅₀ with 50% BC content exhibits best performance with a specific surface area of 138.5 m² g^-1, the saturation magnetization of 27.5 emu g^-1 and CEC value of 53.2 mmol 100 g^-1. The maximum adsorption capacity of Pb²⁺ is 99.5 mg g^-1 based on the Langmuir sorption isotherm study at 298 K, and pseudo-second-order model accurately describes the adsorption process. Regeneration test suggests that MZF-BC₅₀ can be efficiently reused for 6 cycles. In addition, it exhibits a good selective Pb²⁺ and Cd²⁺ removal performance in lead-acid battery wastewater. The results illustrate that this newly developed material has low cost and rapid remediation of Pb²⁺ as good application potential.

Magnetic spent bleaching earth carbon (Mag-SBE@C) for efficient adsorption of tetracycline hydrochloride: Response surface methodology for optimization and mechanism of action

The utilization of spent bleaching earth (SBE)-based materials for adsorption of pollutants from water and wastewater has received growing attention. In this work, a comparative study of magnetic spent bleaching earth carbon (Mag-SBE@C) and spent bleaching earth carbon (SBE@C) was performed to remove tetracycline hydrochloride (TCH) from aqueous solutions. Mag-SBE@C exhibits the larger adsorption capacity (0.238 mmol/g) obtained by the Langmuir model than the original SBE@C (0.150 mmol/g). The adsorption process fits well with the pseudo second-order model and is found to be exothermic (ΔH₀ < 0) and spontaneous (ΔG₀ < 0). The optimal adsorption conditions (Mag-SBE@C dose 2.217 g/L, initial TCH concentration 0.113 mmol/L, initial solution pH 6.533) predicted by the response surface methodology (RSM) are consistent with the actual verification results. The inhibition extents of coexisting cations are ranked in a decline: Al³⁺ > Cu²⁺ > Fe³⁺ > Mg²⁺ > K⁺ > Na⁺. Various characterization results indicate that the adsorption mechanism of TCH by Mag-SBE@C likely includes the π-π interactions, hydrogen bonding, electrostatic interactions, π-cations interactions, FeN covalent bonding, and changes in physical and chemical properties. Mag-SBE@C is easily solid-liquid separated using magnetic field, and can be potentially reused for 13 times before completely losing its activity, exhibiting great potential to antibiotics elimination.

Bone Char Mediated Dechlorination of Trichloroethylene by Green Rust

Biochars function as electron transfer mediators and thus catalyze redox transformations of environmental pollutants. A previous study has shown that bone char (BC) has high catalytic activity for reduction of chlorinated ethylenes using layered Fe(II)-Fe(III) hydroxide (green rust) as reductant. In the present study, we studied the rate of trichloroethylene (TCE) reduction by green rust in the presence of BCs obtained at pyrolysis temperatures (PTs) from 450 to 1050 °C. The reactivity increased with PT, yielding a maximum pseudo-first-order rate constant (k) of 2.0 h^-1 in the presence of BC pyrolyzed at 950 °C, while no reaction was seen for BC pyrolyzed at 450 °C. TCE sorption, specific surface area, extent of graphitization, carbon content, and aromaticity of the BCs also increased with PT. The electron-accepting capacity (EAC) of BC peaked at PT of 850 °C, and EAC was linearly correlated with the sum of concentrations of quinoid, quaternary N, and pyridine-N-oxide groups measured by XPS. Moreover, no TCE reduction was seen with graphene nanoparticles and graphitized carbon black, which have high degrees of graphitization but low EAC values. Further analyses showed that TCE reduction rates are well correlated with the EAC and the C/H ratio (proxy of electrical conductivity) of the BCs, strongly indicating that both electron-accepting functional groups and electron-conducting domains are crucial for the BC catalytic reactivity. The present study delineates conditions for designing redox-reactive biochars to be used for remediation of sites contaminated with chlorinated solvents.

Properties of pellets of torrefied U.S. waste blends

With the continued growing U.S. population, solid waste generation will increase, which will lead to undesired and significant growth in landfilling. Thermal treatment can turn these high calorific value wastes into fuels that can be used in small-to-large power plants. This article focuses on using blends with 40% plastic and 60% fiber wastes and converting them into densified solid fuel by torrefaction and extrusion. The material was torrefied at 300 °C to obtain torrefied samples with different mass losses, ranging from 0% to a maximum of 51%. The torrefaction results showed a clear synergy between plastics and fibers. The torrefied material was then extruded into 9 mm diameter rods and the products were characterized by molecular functional group analysis, thermomechanical analysis, dynamic mechanical analysis, dynamic rheological measurement, density measurement, flexural testing, water absorption test, size distribution measurement, heat content test, and combustion test. The fiber content in the material decreased as mass loss increased, and the process reduced significantly the variability of the material. The heat content increased as the mass loss increased. The plastic in the feedstock acted as a process enabler as it imparted properties like bindability, water resistance, high heat content, and increased degradation reaction rate.

Modified biochar from Moringa seed powder for the removal of diclofenac from aqueous solution

In this study, Moringa seed powder (M_SP) was pyrolyzed at 450 °C to synthesize Moringa seed powder biochar (M_SPB) and treated with phosphoric acid (H₃PO₄) to synthesize phosphate-modified Moringa seed powder biochar (M_SPB-HPO) as an adsorbent for the removal of diclofenac (Dfc) from aqueous solution. Fourier transform infrared (FTIR) analysis, energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and pH point of zero charge (pH_pzc) were conducted to give more insight into the adsorbent's properties. The SEM analysis showed the transformations in the surface morphology from the parent material to the synthesized materials after the thermal and acid treatment. EDS analysis revealed the variation in the elemental composition of the materials prior to and after adsorption of Dfc ions. The FTIR analysis showed changes and peak intensities of functional groups involved in Dfc removal. The pH_pzc showed the charge carried by M_SPB-HPO in different pH conditions. Isotherm data best matched the Sips model, and the pseudo-second-order model best described the adsorption kinetics. The maximum adsorption capacity of M_SPB-HPO by Sips model was found to be 100.876 mg g^-1.

Activity and stability of biochar in hydrogen peroxide based oxidation system for degradation of naphthenic acid

This study investigated the stability and catalytic activity of wheat straw biochar (WS), hardwood biochar (HW) and commercial activated carbon (AC) in hydrogen peroxide (H₂O₂) based oxidation system for degradation of model naphthenic acids compound, 1-methyl-1- cyclohexane carboxylic acid (MCCA). WS showed excellent catalytic activity for decomposition of H₂O₂ and MCCA degradation as demonstrated by high H₂O₂ decomposition rate (2.0*10^-4 M^-1s^-1), amount of hydroxyl (OH) radicals generated (182 mg/L) and degradation efficiency of MCCA (100% at C_o - 100 mg/L). 2-Methyl pentatonic acid was identified as reaction intermediate and 99% mineralization of MCCA was obtained within 4 h. The real wastewater conditions were simulated by addition of chloride (Cl^-) and bicarbonate ions (HCO₃^-) and found that lower concentrations of Cl^- and HCO₃^- have minimal influence on MCCA removal. Overall, biochar catalyzed H₂O₂ based oxidation process has great potential and can be applied for degradation of NAs in oil-sand processed water.

Limited Cu(II) binding to biochar DOM: Evidence from C K-edge NEXAFS and EEM-PARAFAC combined with two-dimensional correlation analysis

Multiple spectroscopic technologies and chemometric analyses were combined to explore the compositional characteristics and Cu binding performance of biochar-derived dissolved organic matter (DOM). The DOM samples were extracted from biochars produced from lignocellulose-rich rapeseed cake (RSC) by pyrolysis at 300, 500, and 700 °C (i.e., RSC300, RSC500, RSC700). Fourier transform infrared spectroscopy (FTIR) and carbon K-edge near-edge X-ray absorption fine structure spectroscopy (NEXAFS) analyses were combined to elucidate the molecular-level C species in the DOM. With the increasing pyrolysis temperature, DOM aromaticity increased, whereas the proportion of metal complexing sites (e.g., carboxyl and phenolic groups) decreased. Fluorescence excitation-emission matrix (EEM) spectroscopy with parallel factor analysis (PARAFAC) indicated that biochar DOM, irrespective of pyrolysis temperature, was mostly composed of three types of humic-like components (C1-C3), and a small amount of a protein-like component (C4). As charring temperature increased, DOM concentrations decreased substantially, but the humic-like C3 with abundant aromatic structures became predominant. Fluorescence quenching experiment and two-dimensional correlation spectroscopy (2D-COS) analysis suggested that the preferential Cu(II) binding fractions of the DOM were the humic-like substances. Moreover, the quenching curve fitting results for individual components indicated that despite the Cu(II) binding affinity was slightly enhanced as the pyrolysis temperature increased, the binding capacities of the four components decreased. In general, the DOM components from RSC biochar exhibited limited Cu(II) binding capacities (2.18-17.7 μmol L^-1). Results from this study improved understanding of the mechanisms by which biochar DOM interacts with Cu, and provided tools for fast screening of biochars to reduce their environmental risks.

Pyrolysis Temperature-Dependent Changes in the Characteristics of Biochar-Borne Dissolved Organic Matter and Its Copper Binding Properties

The dissolved organic matter (DOM) samples from biochars produced from Jerusalem artichoke stalks by pyrolysis at 300, 500, and 700 °C were characterized using a combination of spectroscopic techniques. Additionally, the binding affinities (long K_M) and the complexation capacities (C_L) of the DOM samples with Cu(II) were calculated to assess their Cu binding properties. The biochar-borne DOM contained mainly humic-like components (C1-C3) with a small amount of a protein-like component (C4). As the charring temperature increased, the concentrations of released DOM decreased. The low temperature biochar-borne DOM was found to have more carboxyl groups than its high temperature counterparts, and thus it had larger C_L values. In contrast, the high temperature biochar-borne DOM had larger long K_M values. Low temperature biochars, if applied in a large quantity, would alter copper mobility in the environment because of their high DOM contents and large copper binding capacities.

Enhanced Adsorption of Aqueous Tetracycline Hydrochloride on Renewable Porous Clay-Carbon Adsorbent Derived from Spent Bleaching Earth via Pyrolysis

In this study, spent bleaching earth (SBE) and pyrolyzed SBE (SBE@C) were tested for their capacity to remove tetracycline hydrochloride (TCH) from aqueous solution. The maximum adsorption capacity obtained by the Langmuir model is 0.114 mmol/g for SBE@C and 0.087 mmol/g for SBE. The deleterious effects of coexisting cations were ranked in a decline: Al³⁺ > Mg²⁺ > Na⁺. The results of various characterization methods show that the adsorption mechanisms mainly included π-π interactions, hydrogen bonding, electrostatic interactions, and changes in physical and chemical properties. After 3 repeated cycles of pyrolysis, the adsorption capacity of SBE@C remained at 85.4%, with SBE@C potentially recycled 21 times before complete loss of adsorption capacity. Furthermore, the problem of secondary pollution caused by SBE and residual oil is resolved by the use of SBE@C. All results indicate that SBE@C is a likely candidate for the treatment of TCH wastewater in the coming practical applications.

Developments in biochar application for pesticide remediation: Current knowledge and future research directions

The indiscriminate use of pesticides due to modern agricultural practices has received special attention from the scientific community to address the persistence, recalcitrance and multi-faceted toxicity of several pesticides. Pesticides are hazardous/toxic and can accumulate easily into non-target organisms including humans and other life forms. Several studies have been performed to investigate the effect of biochar addition for pesticide remediation. This review provides a comprehensive information on biochar amendment for the remediation of persistent organic pollutants such as pesticides. The types of pesticides and their hazards to life forms are briefly introduced before detailing biochar production, its characteristics and applications. Biochar addition in pesticide polluted environment offers the following advantages: (a) increases the soil water holding capacity, (b) improves aeration conditions in soil, and (c) provides habitat for the growth of microorganisms, thereby facilitating microbial community for metabolic activities and pesticide degradation. This paper also provides an up-to-date review on remediation of pesticides using biochar, the knowledge gaps and the future research directions in this field to evaluate the effect of biochar addition on agricultural and environmental performances.

Synthesis of novel waste batteries-sawdust-based adsorbent via a two-stage activation method for Pb2+ removal

The novel waste alkaline battery-sawdust-based adsorbents (WABAs) are prepared by a two-stage activation method with the negative electrode materials as activator and different doping ratio of the positive electrode materials and pine sawdust as raw materials. The characteristics of the WABAs are analyzed by SEM, XRD, FT-IR, and specific surface determination (S_BET). The Pb²⁺ adsorption properties of the WABAs are studied by changing the pH of solution, contact time, initial concentration, and temperature. It turns out that when the doping mass ratio is 1:4, the optimum performance of the WABAs is obtained, and comparing with the samples prepared by pure biomass, the iodine adsorption value, total acid groups, and cation exchange capacity (CEC) separately increased by 13, 106, and 22%, respectively. Kinetic studies show that the pseudo-second-order model is more suitable for describing the Pb²⁺ adsorption process and the Langmuir isotherm provides better fitting to the equilibrium data. The thermodynamic parameters indicate the adsorption process would be spontaneous and endothermic. Besides, the prepared WABAs could be reused for 5 cycles with high removal efficiency. This study provides an alternative route for waste alkaline battery treatment. Graphical abstract The schematic diagram of synthesis of waste batteries-sawdust-based adsorbent via a two-stage activation method for Pb²⁺ removal.

Conversion of industrial biowastes to clean solid fuels via hydrothermal carbonization (HTC): Upgrading mechanism in relation to coalification process and combustion behavior

The aim of this work was to study the correlation between dynamic mechanisms of carbon structure associated with their upgrading effects with the help of XPS, ¹³C NMR and 2D-PCIS methods. Results showed the fuel qualifies of biowastes were improved and became comparable to lignite or even bitumite after HTC. The carbon chemical bonds of -C-H and -C-O in biowaste components (mainly protein and polysaccharide) were thermally cracked and enriched in liquid phase in the form of soluble intermediates, which subsequently generated coal-like structures via cyclization as well as polymerization at higher temperatures. The further investigation on thermogravimetric analysis found that the conversion of "-C-H/C-O to aromatic -C-C/CC" was beneficial for stabilizing their combustion behavior by integrating two stages of biowastes (devolatilization stage and combustion stage) into one stage of hydrochars (combustion stage).

Adsorption of low concentration perchlorate from aqueous solution onto modified cow dung biochar: Effective utilization of cow dung, an agricultural waste

In this study, cow dung biochar (CDB) and ferric chloride-modified CDB (Fe@CDB) were synthesized to remove low concentration perchlorate from water. The pseudo-second-order kinetics model was used and satisfactorily described perchlorate removal onto CDB and Fe@CDB. The Langmuir model fit the experimental isotherm data better than the Freundlich model. The maximum adsorption capacity obtained using the Langmuir model was 1787 μg/g for Fe@CDB and 304 μg/g for CDB. The detrimental effects of coexisting anions decreased as: NO₃^- > SO₄^2- > Cl^-. FeCl₃ modification enhanced ion exchange, and this was the main mechanism rather than electrostatic interactions. Also, after modification, the surface area, pore volume, and pore size increased and promoted adsorption. The surface hydrophilicity increased and so did the amounts of the surface oxygenated functional groups OH and COOH, which were responsible for perchlorate adsorption. The materials were further characterized using Brunner-Emmet-Teller (BET) measurements, Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), Scanning Electron Microscopy (SEM), Elemental analysis, X-ray photoelectron spectroscopy (XPS), Boehm titration, Zeta potential and Fourier transform infrared spectroscopy (FTIR).

A Flow Adsorption Microcalorimetry-Logistic Modeling Approach for Assessing Heterogeneity of Brønsted-Type Surfaces: Application to Pyrogenic Organic Materials

Biogeochemical functioning of oxides and pyrogenic organic matter ( pyOM) are greatly influenced by surface and deprotonation characteristics. We present an energetics-based, logistic modeling approach for quantifying surface homogeneity (ϕ_surf) and surface acidity ( pK _a, surf) for Brønsted-type surfaces. The ϕ _surf, pK _a, surf and associated deprotonation behavior of pyOM were quantified across feedstock (honey mesquite, HM; pine, PI; cord grass, CG) and heat-treatment-temperatures (HTT; 200-650 °C). At HTT200, lower ϕ_surf [HM (0.86) > PI (0.61) > CG (0.42)] and higher pK _a, surf [CG (4.4) > PI (4.2) > HM (4.1)] for CG indicated higher heterogeneity and lower acidity for Brønsted-type surface moieties on grass versus wood pyOM. Surface acidity of CG increased at HTT550/650 °C with no effect on ϕ_surf; while the surface heterogeneity of both wood pyOMs increased, the acidity of HM increased and that of PI decreased. Despite different HTT-induced ϕ_surf and pK _a, surf trajectories, the deprotonation range for all pyOM was pH = [Formula: see text]. Therefore, higher heterogeneity pyOMs deprotonate more readily at lower pH, over a wider range and (for similar pK _a,surf and cation exchange capacity) are better cation/metal binding surfaces at pH< pK _a,surf. The approach also facilitates the evaluation of surface and deprotonation characteristics for mixtures and more complex surfaces.

Insight into Multiple and Multilevel Structures of Biochars and Their Potential Environmental Applications: A Critical Review

Biochar is the carbon-rich product of the pyrolysis of biomass under oxygen-limited conditions, and it has received increasing attention due to its multiple functions in the fields of climate change mitigation, sustainable agriculture, environmental control, and novel materials. To design a "smart" biochar for environmentally sustainable applications, one must understand recent advances in biochar molecular structures and explore potential applications to generalize upon structure-application relationships. In this review, multiple and multilevel structures of biochars are interpreted based on their elemental compositions, phase components, surface properties, and molecular structures. Applications such as carbon fixators, fertilizers, sorbents, and carbon-based materials are highlighted based on the biochar multilevel structures as well as their structure-application relationships. Further studies are suggested for more detailed biochar structural analysis and separation and for the combination of macroscopic and microscopic information to develop a higher-level biochar structural design for selective applications.

Pyrolysis of attapulgite clay blended with yak dung enhances pasture growth and soil health: Characterization and initial field trials

Recent studies have shown that the pyrolysis of biomass combined with clay can result in both lower cost and increase in plant yields. One of the major sources of nutrients for pasture growth, as well as fuel and building materials in Tibet is yak dung. This paper reports on the initial field testing in a pasture setting in Tibet using yak dung, biochar, and attapulgite clay/yak dung biochars produced at ratios of 10/90 and 50/50 clay to dung. We found that the treatment with attapulgite clay/yak dung (50/50) biochar resulted in the highest pasture yields and grass nutrition quality. We also measured the properties and yields of mixtures of clay/yak dung biochar used in the field trials produced at 400°C and 500°C to help determine a possible optimum final pyrolysis temperature and dung/clay ratio. It was observed that increasing clay content increased carbon stability, overall biochar yield, pore size, carboxyl and ketone/aldehyde functional groups, hematite and ferrous/ferric sulphate/thiosulphate concentration, surface area and magnetic moment. Decreasing clay content resulted in higher pH, CEC, N content and an enhanced ability to accept and donate electrons. The resulting properties were a complex function of both processing temperature and the percentage of clay for the biochars processed at both 400°C and 500°C. It is possible that the increase in yield and nutrient uptake in the field trial is related to the higher concentration of C/O functional groups, higher surface area and pore volume and higher content of Fe/O/S nanoparticles of multiple oxidation state in the 50/50 clay/dung. These properties have been found to significantly increase the abundance of beneficial microorganisms and hence improve the nutrient cycling and availability in soil. Further field trials are required to determine the optimum pyrolysis production conditions and application rate on the abundance of beneficial microorganisms, yields and nutrient quality.

Applications of biochar in redox-mediated reactions

Biochar is chemically more reduced and reactive than the original feedstock biomass. Graphite regions, functional groups, and redox-active metals in biochar contribute to its redox characteristics. While the functional groups such as phenolic species in biochar are the main electron donating moieties (i.e., reducers), the quinones and polycondensed aromatic functional groups are the components accepting electrons (oxidants). The redox capacity of biochar depends on feedstock properties and pyrolysis conditions. This paper aims to review and summarize the various synthesis techniques for biochars and the methods for probing their redox characteristics. We review the abiotic and microbial applications of biochars as electron donors, electron acceptors, or electron shuttles for pollutant degradation, metal(loid)s (im)mobilization, nutrient transformation, and discuss the underlying mechanisms. Furthermore, knowledge gaps that exist in the exploration and differentiation of the electron transfer mechanisms involving biochars are also identified.