Catalytic Conversion of Glucose into Levulinic Acid Using 2-Phenyl-2-Imidazoline Based Ionic Liquid Catalyst.

Levulinic acid (LA) is an industrially important product that can be catalytically valorized into important value-added chemicals. In this study, hydrothermal conversion of glucose into levulinic acid was attempted using Brønsted acidic ionic liquid catalyst synthesized using 2-phenyl-2-imidazoline, and 2-phenyl-2-imidazoline-based ionic liquid catalyst used in this study was synthesized in the laboratory using different anions (NO3, H2PO4, and Cl) and characterized using 1H NMR, TGA, and FT-IR spectroscopic techniques. The activity trend of the Brønsted acidic ionic liquid catalysts synthesized in the laboratory was found in the following order: [C4SO3HPhim][Cl] > [C4SO3HPhim][NO3] > [C4SO3HPhim][H2PO4]. A maximum 63% yield of the levulinic acid was obtained with 98% glucose conversion at 180 °C and 3 h reaction time using [C4SO3HPhim][Cl] ionic liquid catalyst. The effect of different reaction conditions such as reaction time, temperature, ionic liquid catalyst structures, catalyst amount, and solvents on the LA yield were investigated. Reusability of [C4SO3HPhim][Cl] catalyst up to four cycles was observed. This study demonstrates the potential of the 2-phenyl-2-imidazoline-based ionic liquid for the conversion of glucose into the important platform chemical levulinic acid.

Enabling the valorization of guaiacol-based lignin: Integrated chemical and biochemical production of cis,cis-muconic acid using metabolically engineered Amycolatopsis sp ATCC 39116.

Lignin is nature's second most abundant polymer and displays a largely unexploited renewable resource for value-added bio-production. None of the lignin-based fermentation processes so far managed to use guaiacol (2-methoxy phenol), the predominant aromatic monomer in depolymerized lignin. In this work, we describe metabolic engineering of Amycolatopsis sp. ATCC 39116 to produce cis,cis-muconic acid (MA), a precursor of recognized industrial value for commercial plastics, from guaiacol. The microbe utilized a very broad spectrum of lignin-based aromatics, such as catechol, guaiacol, phenol, toluene, p-coumarate, and benzoate, tolerated them in elevated amounts and even preferred them over sugars. As a next step, we developed a novel approach for genomic engineering of this challenging, GC-rich actinomycete. The successful introduction of conjugation and blue-white screening, using ß-glucuronidase, enabled tailored genomic modifications within ten days. Successive deletion of two putative muconate cycloisomerases from the genome provided the mutant Amycolatopsis sp. ATCC 39116 MA-2, which accumulated 3.1gL-1 MA from guaiacol within 24h, achieving a yield of 96%. The mutant was found also capable to produce MA from a guaiacol-rich true lignin hydrolysate, obtained from pine through hydrothermal conversion. This provides an important proof-of-concept to successfully coupling chemical and biochemical process steps into a value chain from the lignin polymer to an industrial chemical. In addition, Amycolatopsis sp. ATCC 39116 MA-2 was able to produce 2-methyl MA from o-cresol (2-methyl phenol), which opens possibilities towards polymers with novel architecture and properties.

From lignin to nylon: Cascaded chemical and biochemical conversion using metabolically engineered Pseudomonas putida.

Cis,cis-muconic acid (MA) is a chemical that is recognized for its industrial value and is synthetically accessible from aromatic compounds. This feature provides the attractive possibility of producing MA from mixtures of aromatics found in depolymerized lignin, the most underutilized lignocellulosic biopolymer. Based on the metabolic pathway, the catechol (1,2-dihydroxybenzene) node is the central element of this type of production process: (i) all upper catabolic pathways of aromatics converge at catechol as the central intermediate, (ii) catechol itself is frequently generated during lignin pre-processing, and (iii) catechol is directly converted to the target product MA by catechol 1,2-dioxygenase. However, catechol is highly toxic, which poses a challenge for the bio-production of MA. In this study, the soil bacterium Pseudomonas putida KT2440 was upgraded to a fully genome-based host for the production of MA from catechol and upstream aromatics. At the core of the cell factories created was a designed synthetic pathway module, comprising both native catechol 1,2-dioxygenases, catA and catA2, under the control of the Pcat promoter. The pathway module increased catechol tolerance, catechol 1,2-dioxygenase levels, and catechol conversion rates. MA, the formed product, acted as an inducer of the module, triggering continuous expression. Cellular energy level and ATP yield were identified as critical parameters during catechol-based production. The engineered MA-6 strain achieved an MA titer of 64.2 g L-1 from catechol in a fed-batch process, which repeatedly regenerated the energy levels via specific feed pauses. The developed process was successfully transferred to the pilot scale to produce kilograms of MA at 97.9% purity. The MA-9 strain, equipped with a phenol hydroxylase, used phenol to produce MA and additionally converted o-cresol, m-cresol, and p-cresol to specific methylated variants of MA. This strain was used to demonstrate the entire value chain. Following hydrothermal depolymerization of softwood lignin to catechol, phenol and cresols, MA-9 accumulated 13 g L-1 MA and small amounts of 3-methyl MA, which were hydrogenated to adipic acid and its methylated derivative to polymerize nylon from lignin for the first time.

Conversion of Glycerol to Lactic Acid Catalyzed by Different-Sized Cu2O Nanoparticles in NaOH Aqueous Solution.

Different-sized Cu2O nanoparticles with the average particle sizes ranging from 115 to 423 nm were prepared starting from CuSO4 using ascorbic acid as the reductant at room temperature. When Cu2O nanoparticles were used as the catalysts for hydrothermal conversion of glycerol at 230 °C in a NaOH aqueous solution, Cu2O nanoparticles effectively catalyzed the hydrothermal conversion of glycerol to lactic acid as compared to the conventional hydrothermal conversion of glycerol in a "pure" NaOH aqueous solution. Small-sized Cu2O nanoparticles showed higher catalytic activity than the large-sized ones. In a wide glycerol concentration range of 1­2.5 mol/L and a low mole ratio of Cu2O nanoparticle to glycerol of 2.5:100, the glycerol conversion and lactic acid selectivity were more than 86.2% and 87.2%, respectively, after reacting at 230 °C for 2 h.

Catalytic Conversion of Glycerol to Lactic Acid Over Metallic Copper Nanoparticles and Reaction Kinetics.

Different-sized metallic Cu° nanoparticles were prepared by the wet chemical reduction method with organic modifiers. The small-sized Cu° nanoparticles (Cu(PEG)) prepared by using polyethylene glycol as the organic modifier exhibited high catalytic activity for the hydrothermal conversion of glycerol to lactic acid. When the reaction was carried out with the initial glycerol and NaOH concentrations of 1.0 and 1.1 mol L⁻¹ at 230 °C for 4 h, the lactic acid selectivity reached 91.9% at the glycerol conversion of 98.0%. Over CuPEG (36.9 nm) and Cublank (118.3 nm) catalysts, the reaction activation energies were 76.3 and 86.5 kJ mol⁻¹, respectively.

Comparative analysis of pinewood, peanut shell, and bamboo biomass derived biochars produced via hydrothermal conversion and pyrolysis.

Biochars were produced from pinewood, peanut shell, and bamboo biomass through hydrothermal conversion (HTC) at 300 °C and comparatively by slow pyrolysis over a temperature range of 300, 400, and 500 °C. These biochars were characterized by FT-IR, cation exchange capacity (CEC) assay, methylene blue adsorption, as well as proximate and elemental analysis. The experimental results demonstrated higher retained oxygen content in biochars produced at lower pyrolysis temperatures and through HTC, which also correlated to the higher CEC of respective biochars. Furthermore, all types of biochar studied herein were capable of adsorption of methylene blue from solution and the adsorption did not appear to strongly correlate with CEC, indicating that the methylene blue adsorption appears to be dependent more upon the non-electrostatic molecular interactions such as the likely dispersive π-π interactions between the graphene-like sheets of the biochar with the aromatic ring structure of the dye, than the electrostatic CEC. A direct comparison of hydrothermal and pyrolysis converted biochars reveals that biochars produced through HTC have much higher CEC than the biochars produced by slow pyrolysis. Analysis by FT-IR reveals a higher retention of oxygen functional groups in HTC biochars; additionally, there is an apparent trend of increasing aromaticity of the pyrolysis biochars when produced at higher temperatures. The CEC value of the HTC biochar appears correlated with its oxygen functional group content as indicated by the FT-IR measurements and its O:C ratio.

Towards Negative Emissions: Hydrothermal Carbonization of Biomass for Sustainable Carbon Materials.

The contemporary production of carbon materials heavily relies on fossil fuels, contributing significantly to the greenhouse effect. Biomass is a carbon-neutral resource whose organic carbon is formed from atmospheric CO2. Employing biomass as a precursor for synthetic carbon materials can fix atmospheric CO2 into solid materials, achieving negative carbon emissions. Hydrothermal carbonization (HTC) presents an attractive method for converting biomass into carbon materials, by which biomass can be transformed into materials with favorable properties in a distinct hydrothermal environment, and these carbon materials have made extensive progress in many fields. However, the HTC of biomass is a complex and interdisciplinary problem, involving simultaneously the physical properties of the underlying biomass and sub/supercritical water, the chemical mechanisms of hydrothermal synthesis, diverse applications of resulting carbon materials, and the sustainability of the entire technological routes. This review starts with the analysis of biomass composition and distinctive characteristics of the hydrothermal environment. Then, the factors influencing the HTC of biomass, the reaction mechanism, and the properties of resulting carbon materials are discussed in depth, especially the different formation mechanisms of primary and secondary hydrochars. Furthermore, the application and sustainability of biomass-derived carbon materials are summarized, and some insights into future directions are provided.

Clean-up of wastewater discharged from zinc industry through application of zeolite 4A produced from a waste contaminated by lubricant oil components.

The zeolite 4 A powders were sustainably derived from clay-based waste contaminated with the spent lubricant oil. Then, the products were used to treat the wastewater discharged from a local zinc industry. The main challenge is removal of toxic organic components from the waste and conversion of obtained precursor to the zeolite structure, simultaneously. The variation in crystallinity was studied as a function of composition, fusion temperature, aging, and recrystallization times. The zinc adsorption was found to be markedly dependent not only on sodium carbonate/waste ratio but also on aluminum hydroxide content. However, pronounced adsorption was observed over the particles fabricated through the fusion at 900 °C. The relative crystallinity, ∼32 %, is crucial for the effective immobilization of heavy metal ions like Cd2+, Ni2+, and Zn2+ from the wastewater. This level of crystallinity is achievable with the control of aging and recrystallization times, both in 3 h. The maximal zinc adsorption capacity, ∼143 mg g-1, was obtained for the particles with large pores, 48 nm, facilitating the ion diffusion into the adsorbent. On the other hand, the appropriate electrical charge surface expressed based on zeta potential, -43 mV, provided a proper condition for the electrostatic adsorption.

Fundamental properties and phosphorus transformation mechanism of soybean straw during microwave hydrothermal conversion process.

Microwave hydrothermal (MHT) conversion is emerging as a promising technology for the disposal and reutilization of biowastes. This study investigated the fundamental properties and phosphorus transformation mechanism of soybean straw during the MHT conversion process. The oxygen-containing functional groups in soybean straw were stripped, and a trend of dehydration was observed as the temperature increased during the MHT process. Cellulose was identified as the major component of the MHT solid products at high temperature. Glucose and glucuronic acid in the MHT liquid products were gradually converted to formic acid and acetic acid with increasing temperature and holding time. The characteristics of the MHT products directly affected the changes in P speciation and transformation. Most of the P was distributed in liquid products and the impact of holding time was not significant on P distribution at low MHT temperature. With the increase in temperature and holding time, P gradually transferred into the solid products. The proportion of organic phosphorus and soluble inorganic phosphorus in soybean straw was high, and it decreased noticeably after the MHT process. The increase in MHT temperature promoted the conversion of OP and AP into IP and NAIP respectively. P K-edge X-ray absorption near edge structure analysis reveals that Ca5(PO4)3(OH) was the major component of soybean straw and more Ca5(PO4)3(OH) was formed at lower MHT temperature. This study provides fundamental knowledge on the property changes of soybean straw and the transformation of phosphorus during MHT conversion process, which is essential for its disposal and further utilization.

Hydrothermal Transformation of Eggshell Calcium Carbonate into Apatite Micro-Nanoparticles: Cytocompatibility and Osteoinductive Properties.

The eggshell is a biomineral consisting of CaCO3 in the form of calcite phase and a pervading organic matrix (1-3.5 wt.%). Transforming eggshell calcite particles into calcium phosphate (apatite) micro-nanoparticles opens the door to repurposing the eggshell waste as materials with potential biomedical applications, fulfilling the principles of the circular economy. Previous methods to obtain these particles consisted mainly of two steps, the first one involving the calcination of the eggshell. In this research, direct transformation by a one-pot hydrothermal method ranging from 100-200 °C was studied, using suspensions with a stoichiometric P/CaCO3 ratio, K2HPO4 as P reagent, and eggshells particles (Ø < 50 µm) both untreated and treated with NaClO to remove surface organic matter. In the untreated group, the complete conversion was achieved at 160 °C, and most particles displayed a hexagonal plate morphology, eventually with a central hole. In the treated group, this replacement occurred at 180 °C, yielding granular (spherulitic) apatite nanoparticles. The eggshell particles and apatite micro-nanoparticles were cytocompatible when incubated with MG-63 human osteosarcoma cells and m17.ASC murine mesenchymal stem cells and promoted the osteogenic differentiation of m17.ASC cells. The study results are useful for designing and fabricating biocompatible microstructured materials with osteoinductive properties for applications in bone tissue engineering and dentistry.

Two birds with one stone: The multiple roles of hydrothermal treatment in dewatering municipal sludge and producing value-added products.

Sludge dewatering and resource recovery are key steps in the sustainable treatment of municipal sludge (MS) owing to the high levels of moisture and nutrients. Among the treatment options available, hydrothermal treatment (HT) is promising to efficiently improve dewaterability and recover biofuels, nutrients, and materials from MS. However, hydrothermal conversion at different HT conditions generates multiple products. Integrating the characteristics of dewaterability and value-added products under different HT conditions facilitates the application of HT for the sustainable management of MS. Therefore, a comprehensive review of HT for its multiple roles in MS dewatering and value-added resource recovery is conducted. First, the impact of HT temperature on sludge dewaterability and key mechanisms are summarized. Then, this study elucidates the characteristics of biofuels produced (combustible gases, hydrochars, biocrudes, and H2-rich gases), nutrient recovery (proteins and phosphorus), and value-added materials under a wide range of HT conditions. Importantly, along with the integration and evaluation of HT product characteristics under different HT temperatures, this work proposes a conceptual sludge treatment system that integrates the different value-added products in different HT stages. Furthermore, a critical evaluation of the knowledge gaps in the HT for sludge deep dewatering, biofuels, nutrients, and materials recovery is provided along with recommendations for further research.

Hydrothermal conversion of biomass to fuels, chemicals and materials: A review holistically connecting product properties and marketable applications.

Biomass is a renewable and carbon-neutral resource with good features for producing biofuels, biochemicals, and biomaterials. Among the different technologies developed to date to convert biomass into such commodities, hydrothermal conversion (HC) is a very appealing and sustainable option, affording marketable gaseous (primarily containing H2, CO, CH4, and CO2), liquid (biofuels, aqueous phase carbohydrates, and inorganics), and solid products (energy-dense biofuels (up to 30 MJ/kg) with excellent functionality and strength). Given these prospects, this publication first-time puts together essential information on the HC of lignocellulosic and algal biomasses covering all the steps involved. Particularly, this work reports and comments on the most important properties (e.g., physiochemical and fuel properties) of all these products from a holistic and practical perspective. It also gathers vital information addressing selecting and using different downstream/upgrading processes to convert HC reaction products into marketable biofuels (HHV up to 46 MJ/kg), biochemicals (yield >90 %), and biomaterials (great functionality and surface area up to 3600 m2/g). As a result of this practical vision, this work not only comments on and summarizes the most important properties of these products but also analyzes and discusses present and future applications, establishing an invaluable link between product properties and market needs to push HC technologies transition from the laboratory to the industry. Such a practical and pioneering approach paves the way for the future development, commercialization and industrialization of HC technologies to develop holistic and zero-waste biorefinery processes.

Development of bioprocess for corncob-derived levulinic acid production.

Levulinic acid is a significant platform chemical obtained from biomass and can potentially be used to produce value-added biofuels, biopolymers, and biopharmaceuticals. This study aims at statistically optimizing levulinic acid production from agrowastes. Based on the total carbohydrate content (71.93 %), corncob was selected as the target feedstock. A Box-Behnken design with four factors, such as feedstock concentration, reaction time, reaction temperature, and catalyst concentration, was used to optimize the hydrothermal conversion of corncob to levulinic acid at 180 °C for 30 min using 1 M H2SO4 as the acid catalyst and 120 g/L corncob. The maximum yield of 19.9 % was obtained. Additionally, 8.1 g/L formic acid was co-produced. The results of this study can contribute toward valorization of levulinic acid. Moreover, our results can be useful in developing strategies to utilize agrowastes as a renewable feedstock for recent biorefineries to cope with the climate crisis.

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.

Speciation evolution and transformation mechanism of P during microwave hydrothermal process of sewage sludge.

Due to the global shortage of phosphate ore, sewage sludge is an important resource for P recovery. This study aims to investigate how P was migrated and transformed during the microwave hydrothermal (MHT) process of sewage sludge. The effects of MHT and hydrothermal (HT) conversion were compared. The results reveals that there were no significant differences on the P distribution and speciation changes between the HT and MHT products, especially under high hydrothermal temperature. Ortho-P/Pyro-P was the dominant P form in the hydrothermal solid products, and high temperature promoted the transformation of C-O-P to Ortho-P/Pyro-P. The analysis of X-ray absorption near edge structure (XANES) shows that Ca5(PO4)3OH was formed after the hydrothermal processes. The relative abundance of Ca-P decreased first and then increased with increasing hydrothermal temperature. Moderate MHT temperature (170 °C) and holding time (30-60 min) promoted the transformation of P to the liquid products. Generally, the effect of MHT temperature was more significant than that of heating type and holding time on the variations of P distribution and speciations.

Effects of hydrothermal treatment on organic compositions, structural properties, dewatering and biogas production of raw and digested sludge.

The effects of hydrothermal treatment (HTT) under different temperatures and time (120 °C to 250 °C, 10 min to 60 min) on organic matter solubilization and structure changes of secondary sludge (SS) and digested sludge (DS), as well as downstream dewatering and anaerobic digestion were investigated. The results showed that organic matter solubilization increased significantly at 120 °C to 170 °C, then decreased at 200 °C to 250 °C. The organic matter solubilization during HTT showed no obvious difference for two sludge, but for the different organic components. The polysaccharides are easier to be dissolved than protein, which was manifested by the higher dissolution rate at low temperature. The protein was the main soluble component for both of hydrothermal SS and DS, which accounted for 44 % to 64 % of soluble chemical oxygen demand (SCOD). The decrease of residual extracellular polymeric substances (EPS) content and increase of N-acetylglucosamine and DNA concentrations indicated that sludge EPS and cell wall structure were damaged at 170 °C, which contributed to the high organic matter solubilization. Nitrogen balance and molecular weight distribution indicated the concentrations of soluble organic components were the combined result of dissolution and hydrolysis reaction. The hydrolysis and polymerization reaction were intensified at 170 °C to 250 °C, which was verified by the COD balance and molecular weight transformation. The hydrothermal time could further facilitate the organics dissolution and hydrolysis based on the effect of hydrothermal temperature. The EPS structure damage also contributed to the high percentage of free moisture, resulting in enhanced dewaterability. The highest methane production was 298.1 mL CH4/g VSadd for DS hydrothermally treated at 170 °C, which were 125 % and 9.8 % higher than SS and SS-HTT, respectively. This study provided an insight into the general mechanism of HTT and the application of different HTT and AD configurations.

Biobased carbon dots production via hydrothermal conversion of microalgae Chlorella pyrenoidosa.

A promising green hydrothermal process was used to produce biobased nanomaterials carbon dots (CDs) by using microalgae Chlorella pyrenoidosa (CP) and its main model compounds (i.e., glucose, glycine, and octadecanoic acid). The possible reaction pathway including hydrolysis, Amadori rearrangement, cyclization/aromatization, and polymerization was first proposed for the hydrothermal process to produce microalgae-based CDs. Interactions among carbohydrates and proteins in microalgae were vital intermediate reactions in the generation of CDs. The mass yield of CDs reached 7.2% when the CP was hydrothermally treated with 20:1 of liquid-to-solid ratio at 230 °C for 6 h. It was confirmed that nitrogen, sulfur, phosphorous, and potassium were doped onto CP-based CDs (CD-CP) successfully without additional reagents or treatments. The CD-CP yield was 4.0-24.3 times higher than that of model compound-based CDs. Regarding morphology, CD-CP was constituted by many spherical nanoparticles smaller than 20 nm. These CDs emitted blue fluorescence under ultraviolet light, and the fluorescence quantum yield of CD-CP was 4.7-9.4 times higher than that of CP model compound-based CDs. Last, CD-CP displayed broad application prospects as a sensor for Fe3+ detection in wastewater with high sensitivity.

Machine learning prediction of nitrogen heterocycles in bio-oil produced from hydrothermal liquefaction of biomass.

Hydrothermal liquefaction (HTL) of high-moisture biomass or biowaste to produce bio-oil is a promising technology. However, nitrogen-heterocycles (NH) presence in bio-oil is a bottleneck to the upgrading and utilization of bio-oil. The present study applied the machine learning (ML) method (random forest) to predict and help control the bio-oil NH, bio-oil yield, and N content of bio-oil (N_oil). The results indicated that the predictive performance of the yield and N_oil were better than previous studies, achieving test R2 of 0.92 and 0.95, respectively. Acceptable predictive performance (test R2 of 0.82 and RMSE of 7.60) for the prediction of NH was also achieved. The feature importance analysis, partial dependence, and Shapely value were used to interpret the prediction models and study the NH formation mechanisms and behavior. Then, forward optimization of NH was implemented based on optimal predictive models, indicating the high potential of ML-aided bio-oil production and engineering.

Hydrothermal treatment as a complementary tool to control the invasive Pampas grass (Cortaderia selloana).

The rapid spread of invasive Pampas grass (PG) is having not only ecosystems impact, but also significant economic and social effects. The tonnes of bulky waste from the plant disposal require proper treatment to avoid seed dispersal, greenhouse gas emissions and landscape damage. In the pursuit of zero-waste management, hydrothermal treatment (HT) appears as a challenging alternative. The possibility of mobile HT systems offers an alternative to accomplish on-site both the PG waste management and the application of the resulting by-products within a circular framework. As a first step, this research shows that, without a prior drying step, the hydrothermal treatment at 100-230 °C under autogenous water vapor pressure for only 30 min allows safe seeds inertization, while a stable carbon-enriched solid and an aqueous stream are generated. Prolonging the process for 2 h has no profitable effects. As the reaction temperature increases, the PG residue is converted into a material with 49-58 wt% of carbon, 41-32 wt% of oxygen and 3-4 wt% of ash. The pH (~6.3), low electrical conductivity (1.21-0.86 dS/m), high carbon content, open porosity (5-8 m2/g) and improved performance in seed germination and in the early growth test suggest the potential of HT-solids derived at 100-120 °C as amendment to sequester carbon in the soil and improve its physico-biological properties. The phytotoxicity detected in the peat/lignite-like solids obtained at 200-230 °C limits its application in soil, but calorific values of 22-24 MJ/kg indicate their suitability as CO2-neutral fuel. The agrochemical analysis of the liquid by-products indicates poor value on their own, but their use supplemented with compost may be an option.

Arsenic removal via a novel hydrochar from livestock waste co-activated with thiourea and γ-Fe2O3 nanoparticles.

Arsenic (As) contaminants post tremendous threats to environment safety. Pristine hydrochar (PHC), thiourea-activated hydrochar (THC), and thiourea-Fe(NO3)3-activated hydrochar (Fe2O3@THC) were fabricated from dairy cattle manure via one-pot hydrothermal carbonization at 250 â„ƒ and applied for aqueous As(V) removal. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize hydrochars and As(V) adsorption. Thiourea increased N and S functional groups (-NH2, C-N, C=S and S=O). Fe(NO3)3 introduced γ-Fe2O3 nanoparticles and provided Fe2O3@THC with Fe-O. The combination of thiourea and Fe(NO3)3 granted Fe2O3@THC with the largest surface area (33.45 m2/g), and the highest total pore volume (0.095 cm3/g) among three hydrochars. As(V) adsorption was a physicochemical process involving electrostatic attraction, complexation, ion exchange and H-bond interaction. The maximum As(V) adsorption capacities and partition coefficients decreased as follows: Fe2O3@THC (44.80 mg/g; 38.44 L/g) > THC (38.77 mg/g; 5.94 L/g) > PHC (19.05 mg/g; 1.17 L/g). Three hydrochars exhibited preferable reusability in NaOH solution with only 24.2%, 11.8% and 14.1% decrease in adsorption rates after four cycles for PHC, THC and Fe2O3@THC, respectively. Fe2O3@THC is a promising adsorbent for efficient As(V) removal. This study explored the efficient As(V) removal by activated hydrochars with future research potential.