One-pot synthesis and characterization of engineered hydrochar by hydrothermal carbonization of biomass with ZnCl2

Utilization of peanut hull hydrochar /beta cyclodextrin/Fe3O4 magnetic composite for lead ion removal from water solution

This study involves synthesizing peanut hull hydrochar (PHH) and a PHH/β-CD/Fe3O4 magnetic composite through hydrothermal and chemical precipitation methods, respectively, to use as effective adsorbents for Pb2+ removal. Vibrating-sample magnetometry (VSM) and Brunauer-Emmett-Teller (BET) analyses revealed that the magnetic saturation value and specific active surface area of PHH/β-CD/Fe3O4 are 31.543 emu/g and 32.123 m2/g, respectively. The impact of key variables on adsorption efficiency was evaluated using the response surface method - central composite design. ANOVA results (F-value: 166.22 and p-value: <0.05) demonstrated that the model effectively assesses the interaction of variables in the adsorption process. Additionally, R2, Adjusted R2, and Predicted R2 values were 0.999, 0.986, and 0.975, respectively, indicating the model's high adequacy in describing response changes. The maximum efficiency for Pb2+ adsorption was found to be 95.35% using PHH and 99.73% with the PHH/β-CD/Fe3O4 magnetic composite. These measurements were taken at a temperature of 25 °C, an adsorbent dose of 1 g/L, a pH of 6, and a Pb2+ concentration of 5 mg/L, with respective contact times of 130 min and 50 min. Thermodynamic analysis revealed negative enthalpy and Gibbs free energy values, indicating that the adsorption process is exothermic and spontaneous. The negative entropy parameter suggests a reduction in random interactions during the process. The Pb2+ adsorption data for both PHH (R2: 0.982) and PHH/β-CD/Fe3O4 (R2: 0.985) were best described by the Pseudo 2nd order kinetic model. Equilibrium data followed the Freundlich model, with R2 values of 0.981 for PHH and 0.990 for PHH/β-CD/Fe3O4, highlighting the importance of heterogeneous surfaces in the removal process. The maximum adsorption capacities for Pb2+ were 26.72 mg/g for PHH and 33.88 mg/g for PHH/β-CD/Fe3O4. Reuse and stability tests confirmed the structural stability and reusability of the adsorbents. Therefore, the PHH/β-CD/Fe3O4 magnetic composite is a promising option for removing Pb2+ from aqueous solutions.

Hydrochar as a bio-based adsorbent for heavy metals removal: A review of production processes, adsorption mechanisms, kinetic models, regeneration and reusability

The spread of heavy metals throughout the ecosystem has extremely endangered human health, animals, plants, and natural resources. Hydrochar has emerged as a promising adsorbent for removal of heavy metals from water and wastewater. Hydrochar, obtained from hydrothermal carbonization of biomass, owns unique physical and chemical properties that are highly potent in capturing heavy metals via surface complexation, electrostatic interactions, and ion exchange mechanisms. This review focuses on removing heavy metals by hydrochar adsorbents from water bodies. The article discusses factors affecting the adsorption capacity of hydrochars, such as contact time, pH, initial metal concentration, temperature, and competing ions. Literature on optimization approaches such as surface modification, composite development, and hybrid systems are reviewed to enlighten mechanisms undertaking the efficiency of hydrochars in heavy metals removal from wastewater. The review also addresses challenges such as hydrochar regeneration and reusability, alongside potential issues related to its disposal and metal leaching. Integration with current water purification methods and the significance of ongoing research and initiatives promoting hydrochar-based technologies were also outlined. The article concludes that combining hydrochar with modern technologies such as nanotechnology and advanced oxidation techniques holds promise for improving heavy metal remediation. Overall, this comprehensive analysis provides valuable insights to guide future studies and foster the development of effective, affordable, and environmentally friendly heavy metal removal technologies to ensure the attainment of safer drinking water for communities worldwide.

In-situ remediation of cadmium contamination in paddy fields: from rhizosphere soil to rice kernel

Cadmium (Cd) has become an important heavy metal pollutant because of its strong migration and high toxicity. The industrial production process aggravated the Cd pollution in rice fields. Human exposure to Cd through rice can cause kidney damage, emphysema, and various cardiovascular and metabolic diseases, posing a grave threat to health. As modern technology develops, the Cd accumulation model in rice and in-situ remediation of Cd pollution in cornfields have been extensively studied and applied, so it is necessary to sort out and summarize them systematically. Therefore, this paper reviewed the primary in-situ methods for addressing heavy metal contamination in rice paddies, including chemical remediation (inorganic-organic fertilizer remediation, nanomaterials, and composite remediation), biological remediation (phytoremediation and microbial remediation), and crop management remediation technologies. The factors that affect Cd transformation in soil and Cd migration in crops, the advantages and disadvantages of remediation techniques, remediation mechanisms, and the long-term stability of remediation were discussed. The shortcomings and future research directions of in situ remediation strategies for heavily polluted paddy fields and genetic improvement strategies for low-cadmium rice varieties were critically proposed. To sum up, this review aims to enhance understanding and serve as a reference for the appropriate selection and advancement of remediation technologies for rice fields contaminated with heavy metals.

How can heteroatoms boost the performance of photoactive nanomaterials for wastewater purification?

Photocatalysis, as an alternative for treating persistent water pollutants, holds immense promise. However, limitations hinder sustained treatment and recycling under varying light conditions. This comprehensive review delves into the novel paradigm of metal and non-metal doping to overcome these challenges. It begins by discussing the fundamental principles of photocatalysis and its inherent limitations. Understanding these constraints is crucial for developing effective strategies. Band gap narrowing by metal and non-metal doping modifies the band gap, enabling visible-light absorption. Impurity energy levels and oxygen vacancies influenced the doping energy levels and surface defects. Interfacial electron transfer and charge carrier recombination are the most important factors that impact overall efficiency. The comparative analysis of nanomaterials are reviewed on various, including nanometal oxides, nanocarbon materials, and advanced two-dimensional structures. The synthesis process are narratively presented, emphasizing production yields, selectivity, and efficiency. The review has potential applications in the environment for efficient pollutant removal and water purification, economic cost-effective and scalable production and technological advancement catalyst design, in spite of its challenges in material stability, synthesis methods and optimizing band gaps. The novelty of the review paper is on the proposal of a new paradigm of heterojunctions of doped metal and non-metal photocatalysts to promise highly efficient water treatment. This review bridges the gap between fundamental research and practical applications, offering insights into tailored nano photocatalysts.

Insights into the Mechanism of Efficient Cr(VI) Removal from Aqueous Solution by Iron-Rich Wheat Straw Hydrochar: Coupling DFT Calculation with Experiments

Agricultural solid waste has become one of the raw materials for hydrothermal carbon production, promoting resource utilization. This study synthesized two types of ball-milling carbons (Fe-MHBC vs MHBC) with and without FeCl3 modification using wheat straw hydrochars. Cr(VI) adsorption on these two types of ball-milling carbons was investigated. According to Langmuir's maximum adsorption capacity analysis, Fe-MHBC had a capacity of 116.29 mg g-1. The thermodynamic analysis based on isothermal adsorption reveals the spontaneous process of the reaction between the two materials. The adsorption of Cr(VI) on Fe-MHBC exhibited excellent agreement with the pseudo-second-order kinetics model. Furthermore, X-ray photoelectron spectroscopy analysis showed that Fe(II) in the material reduced Cr(VI) when it participated in the reaction. The acidic conditions facilitate the elimination of Cr(VI). The Fe-MHBC has a higher zeta potential, which enhances the electrostatic attraction of Cr(VI) particles. Even with a starting pH of 10, the removal rate can be consistently maintained at over 64%. The adsorption of Cr(VI) was inhibited by various anions and higher ion concentrations. Density functional theory demonstrates that the presence of Fe enhances the adsorption capacity and electron transfer flux of Cr(VI). Fe-MHBC effectively eliminates Cr(VI) by the process of electrostatic adsorption, redox, and complexation reactions. This study demonstrated that hydrochar materials modified by FeCl3 through a ball-milling process show considerable potential as effective adsorbents in the treatment of Cr(VI) pollution, offering a viable and environmentally friendly solution for mitigating this prevalent environmental issue.

A novel approach for the facile synthesis of zinc oxide/carbon hybrid systems from corn distillers soluble: Surface modification and characterization for sustainable remediation

Sustainable, efficient, and environmentally friendly ways to tailor the carbonaceous materials from bio sources with desired functionalities remain a challenge around the world. In this study, we represent a novel approach to synthesize carbon hybrid material based on Zinc Oxide/carbon (ZnO/C) hybrid systems by catalytic hydrothermal process via crosslinking reaction through nucleation and growth of ZnO particles at the functional groups of oxidized carbon material. This research explored the volarization of Condensed Corn Distillers Soluble (CDS) as a carbon precursor to synthesize biobased carbon spheres. Surface modification of the produced carbon spheres took place using zinc chloride (ZnCl2) during hydrothermal carbonization (HTC). Zinc chloride (ZnCl2) was used to function as a catalyst during HTC and functioned as a ZnO source to synthesize (ZnO/C) hybrid systems. Design Expert software v13 was used to design the hydrothermal carbonization (HTC) experiments and response surface methodology was used to find the optimized conditions for the preparation of carbon hybrid systems. The hydrothermal synthesis process introduced 3D stone like zinc oxide particles onto the carbon matrix. These particles were self-assembled onto the carbon framework to produce carbon hybrid systems with unique physical, chemical, structural and functional properties. Herein, the obtained carbon hybrid systems (ZnO/C) were investigated and discussed in detail. ZnO/C hybrid systems were analyzed for surface morphology using scanning electron microscopy (SEM) that presented a 3D spherical interconnected phase and XRD analyses were used for phase crystallinity that showed new crystalline phases such as hopeite and zincite after the ZnCl2 incorporation. Surface functional groups were also analyzed by FTIR and results confirmed the presence of hydrophilic groups such as -OH, CC, and COOH on the surface of ZnO/C hybrid carbon systems. This study provided the insightful guidance for tailoring novel design of multifunctional carbon material as an adsorbent/catalyst for various applications of sustainable remediation.

Activated carbons-preparation, characterization and their application in CO2 capture: A review

In this paper, we provide a comprehensive review of the latest research trends in terms of the preparation, and characteristics of activated carbons regarding CO2 adsorption applications, with a special focus on future investigation paths. The reported current research trends are primarily closely related to the synthesis conditions (carbonization and physical or chemical activation process), to develop the microporosity and surface area, which are the most important factors affecting the effectiveness of adsorption. Furthermore, we emphasized the importance of regeneration techniques as a factor determining the actual technological and economic suitability of a given material for CO2 capture application. Consequently, this work provides a summary and potential directions for the development of activated carbons (AC). We attempt to create a thorough theoretical foundation for activated carbons while also focusing on identifying and specific statements of the most relevant ongoing research scope that might be advantageous to progress and pursue in the coming years.

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.

Waste-derived carbon nanostructures (WD-CNs): An innovative step toward waste to treasury

With the growing population, the accumulation of waste materials (WMs) (industrial/household waste) in the environment incessantly increases, affecting human health. Additionally, it affects the climate and ecosystem of terrestrial and water habitats, thereby needing effective management technology to control environmental pollution. In this aspect, managing these WMs to develop products that mitigate the associated issues is necessary. Researchers continue to focus on WMs management by adopting a circular economy. These WMs convert into useful/value-added products such as polymers and nanomaterials (NMs), especially carbon nanomaterials (CNs). The conversion/transformation of waste material into useful products is one of the best solutions for managing waste. Waste-derived CNs (WD-CNs) have established boundless promises for numerous applications like environmental remediation, energy, catalysts, sensors, and biomedical applications. This review paper discusses the several sources of waste material (agricultural, plastic, industrial, biomass, and other) transforming into WD-CNs, such as carbon nanotubes (CNTs), biochar, graphene, carbon nanofibers (CNFs), carbon dots, etc., are extensively elaborated and their application. The impact of metal doping within the WD-CNs is briefly discussed, along with their applicability to end applications.

In-situ synthesis of ZIF-8 on magnetic pineapple leaf biochar as an efficient and reusable adsorbent for methylene blue removal from wastewater

The presence of organic dyes in aquatic systems poses a significant threat to ecosystems and human well-being. Due to recycling challenges, traditional commercial activated carbon is not cost-effective. To address this, an imidazolate acid zeolite framework-8 (ZIF-8)-modified magnetic adsorbent (ZMPLB-800) was synthesized through the in-situ formation of ZIF-8 and subsequent carbonization at 800 °C, using magnetic pineapple leaf biochar (MPLB) as a carrier. The porous structure of ZMPLB-800 facilitates the rapid passage of dye molecules, enhancing adsorption performance. ZMPLB-800 exhibited remarkable adsorption capacity for methylene blue (MB) across a pH range of 3-13, with a maximum adsorption capacity of 455.98 mg g-1. Adsorption kinetics and thermodynamics followed the pseudo-second-order kinetic model and Langmuir isotherm model. Mechanisms of MB adsorption included pore filling, hydrogen bonding, electrostatic interactions, π-π interactions, and complexation through surface functional groups. Additionally, ZMPLB-800 demonstrated excellent regeneration performance, recording a removal efficiency exceeding 87% even after five adsorption/desorption cycles. This study provides a novel strategy for treating dye wastewater with MOF composites, laying the foundation for waste biomass utilization.

Rice husk hydrochar prepared by hydrochloric acid assisted hydrothermal carbonization for levofloxacin removal in bioretention columns

Hydrochars are promising adsorbents in pollutant removal for water treatment. Herein, hydrochloric acid (HCl) co-hydrothermally treated hydrochars were prepared from rice husk biomass at 180 °C via a one-step hydrothermal method. Adsorption behaviors of levofloxacin (LVX) on hydrochars were evaluated. The specific surface area and pore volume of the hydrochar synthesized in 5 mol/L HCl (5H-HC) were almost 17 and 8 times of untreated hydrochar, respectively. The 5H-HC sample exhibited the highest LVX adsorption capability at room temperature (107 mg/g). Thermodynamic experimental results revealed that adsorption was a spontaneous endothermic process. Yan model provided the best description of the breakthrough behavior of LVX in bioretention column, indicating that the adsorption on the samples involved several rate-limiting factors including diffusion and mass transfer. The results show that facile HCl co-hydrothermal carbonization of waste biomass can produce novel hydrochars with high LVX adsorption ability.

Impacts of kaolinite enrichment on biochar and hydrochar characterization, stability, toxicity, and maize germination and growth

In this study, biochar (BC) and hydrochar (HC) composites were synthesized with natural kaolinite clay and their properties, stability, carbon (C) sequestration potential, polycyclic aromatic hydrocarbons (PAHs) toxicity, and impacts on maize germination and growth were explored. Conocarpus waste was pretreated with 0%, 10%, and 20% kaolinite and pyrolyzed to produce BCs (BC, BCK10, and BCK20, respectively), while hydrothermalized to produce HCs (HC, HCK10, and HCK20, respectively). The synthesized materials were characterized using X-ray diffraction, scanning electron microscope analyses, Fourier transform infrared, thermogravimetric analysis, surface area, proximate analyses, and chemical analysis to investigate the distinction in physiochemical and structural characteristics. The BCs showed higher C contents (85.73-92.50%) as compared to HCs (58.81-61.11%). The BCs demonstrated a higher thermal stability, aromaticity, and C sequestration potential than HCs. Kaolinite enriched-BCs showed the highest cation exchange capacity than pristine BC (34.97% higher in BCK10 and 38.04% higher in BCK20 than pristine BC), while surface area was the highest in kaolinite composited HCs (202.8% higher in HCK10 and 190.2% higher in HCK20 than pristine HC). The recalcitrance index (R50) speculated a higher recalcitrance for BC, BCK10, and BCK20 (R50 > 0.7), minimal degradability for HCK10 and HCK20 (0.5 < R50 < 0.7), and higher degradability for biomass and HC (R50 < 0.5). Overall, increasing the kaolinite enrichment percentage significantly enhanced the thermal stability and C sequestration potential of charred materials, which may be attributed to changes in the structural arrangements. The ∑ total PAHs concentration in the synthesized materials were below the USEPA's suggested limits, indicating their safe use as soil amendments. Germination indices reflected positive impacts of synthesized charred materials on maize germination and growth. Therefore, we propose that kaolinite-composited BCs and HCs could be considered as efficient and cost-effective soil amendments for improving plant growth.

Fabrication of Iron-Containing Biochar by One-Step Ball Milling for Cr(VI) and Tetracycline Removal from Wastewater

Simple ball milling technology can simultaneously improve the adsorption performance of adsorbents for heavy metals and organic pollutants and has attracted increasing attention. Iron-modified biochar (Fe@MBC) was prepared by one-step ball milling, and the characterization results proved that FeCl3 was successfully loaded on biochar. The removal rates of Cr(VI) and tetracycline hydrochloride (TC) by Fe@MBC were increased by 88.27% and 82.64% compared with BC. The average pore size, oxygen-containing functional groups and graphitization degree of Fe@MBC are higher than those of BC, which is more conducive to promoting adsorption. The adsorption isotherms show that the adsorption of Cr(VI) and TC on the Fe@MBC surface conforms to the Langmuir type of single-layer adsorption and the Freundlich model of multilayer adsorption, respectively. The maximum adsorption capacities of Cr(VI) and TC are 25.46 and 66.91 mg·g-1, respectively. Kinetic experiments show that the adsorption process is more consistent with the pseudo-second-order model of chemical adsorption. The adsorption process of Cr(VI) and TC on the Fe@MBC surface is a spontaneous endothermic process that becomes more obvious as the temperature increases. The increase in solution pH has a significant impact on the removal rate of Fe@MBC. When the pH value increased from 3 to 11, the adsorption rates decreased by 53.74% and 17.16%, respectively. The presence of PO43-, CO32-, K+, and Cu2+ significantly affects the adsorption of TC by Fe@MBC, and PO43- and CO32- also affect the adsorption of Cr(VI). Mechanistic studies show that ion exchange, electrostatic interaction, pore filling, and hydrogen bonding contribute to the removal of Cr(VI) and TC by Fe@MBC. The removal mechanism of Cr(VI) also involves complexation and redox reactions, and the removal mechanism of TC involves π-π bonds and van der Waals forces. The results show that Fe@MBC is a green and efficient adsorbent.

Removing DOM from chloride modified hydrochar could improve Cu2+ adsorption capacity from aqueous solution

The behavior and composition of hydrochar-based dissolved organic matter (DOM) would affect the efficiency of copper (Cu) removal from wastewater through adsorption. In this study, the reed was hydrolyzed in the presence of feedwater with and without ZnCl2, FeCl3, and SnCl4 to produce pristine hydrochars (PHCs), which were named H2O-HC, ZnCl2-HC, FeCl3-HC, and SnCl4-HC. After removal of DOM, washed hydrochars (WHCs) were obtained, labelled as W-H2O-HC, W-ZnCl2-HC, W-FeCl3-HC, and W-SnCl4-HC. The release dynamics of DOM from PHCs were analyzed, and the adsorption behaviors of Cu2+ on both PHCs and WHCs were investigated. The results showed that chloride-modifications were beneficial for the porosity, specific surface area (SSA), and functional groups of WHCs. Meanwhile, the quantity of hydrochar-based DOM was significantly affected by chloride-modifications. In particular, the relative contents of Ar-P and Fa-L in the DOM released from hydrochars varied with time and modification. Furthermore, the Qe of Cu2+ adsorption on WHCs followed the order of W-SnCl4-HC > W-FeCl3-HC > W-ZnCl2-HC > W-H2O-HC at 15 °C. Compared to PHCs, the adsorption capacity of Cu2+ on WHCs was improved by 7.15-119.77% at the temperature of 35 °C. Simultaneously, the adsorption capacity of Cu2+ in WHCs showed a significant correlation with the SSA via physical adsorption (P < 0.05). Moreover, XPS analysis revealed that Cu2+ adsorption also occurred via complexation and chelation through newly formed Cu-O group between W-SnCl4-HC and Cu2+. Notably, the increase of Cu2+ adsorption in WHCs was significantly correlated with the release of Fa-L and Ar-P from PHCs (P < 0.05). This study found that the content and composition of hydrochar-based DOM could be a major driving factor for Cu2+ adsorption.

Energy recovery from agro-forest wastes through hydrothermal carbonization coupled with hydrothermal Co-gasification: Effects of succinic acid on hydrochars and H2 production

Aiming to upgrade agro-forest wastes into value-added solid and gaseous fuels in the present investigation, hydrothermal carbonization (HTC) of spruce (SP), canola hull (CH), and canola meal (CM) was optimized in terms of operating conditions, maximizing the higher heating value of hydrochars. The optimal operating conditions were achieved at HTC temperature, reaction time, and solid-to-liquid ratio of 260 ^°C, 60 min, and 0.2 g mL^-1, respectively. At the optimum condition, succinic acid (0.05-0.1 M) was used as HTC reaction medium to investigate the effects of acidic medium on the fuel characteristics of hydrochars. The succinic acid assisted HTC was found to eliminate ash-forming minerals e.g., K, Mg, and Ca from hydrochar backbones. The calorific values, H/C and O/C atomic ratios of hydrochars were in the range of 27.6-29.8 MJ kg^-1, 0.8-1.1, and 0.1-0.2, respectively, indicating the biomass upgrading into coal-like solid fuels. Finally, hydrothermal gasification of hydrochars with their corresponding HTC aqueous phase (HTC-AP) was assessed. Gasification of CM resulted in a relatively high H₂ yield of 4.9-5.5 mol kg^-1 followed by that for SP with 4.0-4.6 mol H₂ per kg of hydrochars. Results suggest that hydrochars and HTC-AP have a great potential for H₂ production via hydrothermal co-gasification, while suggesting HTC-AP reuse.

Methylene Blue Dye Adsorption on Iron Oxide-Hydrochar Composite Synthesized via a Facile Microwave-Assisted Hydrothermal Carbonization of Pomegranate Peels' Waste

The toxicity of dyes has a long-lasting negative impact on aquatic life. Adsorption is an inexpensive, simple, and straightforward technique for eliminating pollutants. One of the challenges facing adsorption is that it is hard to collect the adsorbents after the adsorption. Adding a magnetic property to the adsorbents makes it easier to collect the adsorbents. The current work reports the synthesis of an iron oxide-hydrochar composite (FHC) and an iron oxide-activated hydrochar composite (FAC) through the microwave-assisted hydrothermal carbonization (MHC) technique, which is known as a timesaving and energy-efficient method. The synthesized composites were characterized using various techniques, such as FT-IR, XRD, SEM, TEM, and N2 isotherm. The prepared composites were applied in the adsorption of cationic methylene blue dye (MB). The composites were formed of crystalline iron oxide and amorphous hydrochar, with a porous structure for the hydrochar and a rod-like structure for the iron oxide. The pH of the point of zero charge (pHpzc) of the iron oxide-hydrochar composite and the iron oxide-activated hydrochar composite were 5.3 and 5.6, respectively. Approximately 556 mg and 50 mg of MB dye was adsorbed on the surface of 1 g of the FHC and FAC, respectively, according to the maximum adsorption capacity calculated using the Langmuir model.

Nitrated hydrochar reduce the Cd accumulation in rice and shift the microbial community in Cd contaminated soil

Rice grown on Cd-contaminated soil may accumulate Cd in grain, which is extremely harmful to human health. Several managements are developed to reduce the Cd load in rice, while in-situ immobilization by soil amendments has been attractive for its feasibility. Waste-derived hydrochar (HC) has been shown effective at immobilizing Cd in soil. However, potential plant negative effects and huge application amount are crucial to resolving in extensive application of HC. Nitric acid ageing may be an effective method to deal with these problems. In this paper, HC and nitrated hydrochar (NHC) were added to the Cd-contaminated soil at rates of 1% and 2% in a rice-soil column experiment. Results showed that NHC markedly promoted root biomass of rice by 58.70-72.78%, whereas HC had effects of 35.86-47.57%. Notably, NHC at 1% reduced the accumulation of Cd in rice grain, root and straw by 28.04%, 15.08% and 11.07%, respectively. A consistent decrease of 36.30% in soil EXC-Cd concentration was caused by NHC-1%. Following soil microbial community was shifted greatly under HC and NHC applications. The relative abundance of Acidobacteria was decreased by 62.57% in NHC-2% and by 56.89% in HC-1%. Nevertheless, Proteobacteria and Firmicutes were promoted by NHC addition. In contrast to HC, co-occurrence network of dominated bacteria was more complex and centralized generated by NHC. Key bacteria in that metabolic network of NHC such as Anaerolineae and Archangiaceae played key roles in Cd immobilization. These observations verified that NHC was more efficient to decrease Cd accumulation in rice and could alleviate the negative roles to plant by microbial changings in community composition and network. It could provide an enrichment of paddy soil microbial responds to the interaction of NHC with Cd and lay a foundation for the remediation of Cd-contaminated soil by NHC.

Directional regulation and mechanism analysis of the surface properties of hydrothermal carbon by circulating liquid in the hydrothermal carbonization procedure

The complexity of the chemistry behind the hydrothermal conversion is enormous. Components interact with their own physical and chemical structure, making it harsh to understand the conversion as a whole. Herein, the six-water recirculation and loading nano SiO₂ experiment in a one-pot hydrothermal carbonization procedure was designed to elucidate the mechanism of regulating the functional groups and microporous structure of the hydrochar surface. The hydrochar prepared by the second circulating liquid and loading nano-SiO₂ (HBC-R2/Si) was equipped most enriched functional groups (carboxyl = 11.48 μmol/g, phenolic hydroxyl = 52.98 μmol/g, lactone groups = 46.52 μmol/g) and suitable pore size (1.90 nm-1.93 nm) as a sorbent riched in hemicellulose. The sorption kinetics (equilibrium reached ≈ 480 min) are approximately evenly fitted by the pseudo-second-order, Weber and Morris, and Elovich models, indicating that membranes and particles diffusion, pore diffusion, and surface sorption coexisted in the sorption of methylene blue (MB) on the hydrochar materials. Simultaneously, all hydrochar materials achieved over 25% MB removal within 90 min (liquid membrane diffusion) and over 40% for HBC-R2 and HBC-R2/Si, suggesting that liquid membrane diffusion is the predominant rate-limiting step. Pearson's correlation analysis and Mantel's analysis announced that the cation exchange capacity (CEC), pore size, and carboxyl groups on the hemicellulose affect the sorption capacity by limiting the pore diffusion procedure. However, the CEC and the phenolic hydroxyl groups on the cellulose and hemicellulose affect the sorption rate by limiting membrane diffusion. Three consecutive sorption/desorption cycles confirmed the high stability and reusability of HBC-R2/Si composites.

Co-Carbonized Waste Polythene/Sugarcane Bagasse Nanocomposite for Aqueous Environmental Remediation Applications

The conversion of worthless municipal solid wastes to valuables is a major step towards environmental conservation and sustainability. This work successfully proposed a technique to utilize the two most commonly available municipal solid wastes viz polythene (PE) and sugarcane bagasse (SB) for water decolorization application. An SBPE composite material was developed and co-pyrolyzed under an inert atmosphere to develop the activated SBPEAC composite. Both SBPE and SBPEAC composites were characterized to analyze their morphological characteristics, specific surface area, chemical functional groups, and elemental composition. The adsorption efficacies of the composites were comparatively tested in the removal of malachite green (MG) from water. The SBPEAC composite had a specific surface area of 284.5 m²/g and a pore size of ~1.33 nm. Batch-scale experiments revealed that the SBPEAC composite performed better toward MG adsorption compared to the SBPE composite. The maximum MG uptakes at 318 K on SBPEAC and SBPE were 926.6 and 375.6 mg/g, respectively. The adsorption of MG on both composites was endothermic. The isotherm and kinetic modeling data for MG adsorption on SBPEAC was fitted to pseudo-second-order kinetic and Langmuir isotherm models, while Elovich kinetic and D-R isotherm models were better fitted for MG adsorption on SBPE. Mechanistically, the MG adsorption on both SBPE and SBPEAC composites involved electrostatic interaction, H-bonding, and π-π/n-π interactions.

Hydrothermal carbonization of cow dung with human urine as a solvent for hydrochar: An experimental and kinetic study

Hydrothermal carbonization (HTC) is the most cost-effective, environmentally friendly, and efficient physicochemical and biochemical process for converting biomass to products with added value. The objective and novelty of this work is to produce and investigate the qualities of hydrochar fuel (as a solid fuel) from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel (i.e., coal). HTC based studies were conducted in batch, at three different reaction temperatures (180 °C, 200 °C, and 220 °C) and two different reaction periods (2 and 4 h). For kinetic analysis and reaction mechanism of the combustion behavior of the produced hydrochar, the model free kinetic methods and the z-master plot were used. From the model free kinetics methods, it was observed that the resultant optimum average activation energy and pre-exponential factor for the produced hydrochar at 180 °C and 2 h reaction period (HTC_180_2) were ∼120 kJ/mol and ∼5.59 × 10²⁵ sec^-1, respectively. In addition, the little variation between ΔE_α and ΔH_α (∼10 kJ/mol) suggests that the combustion of produced hydrochar (HTC_180_2) occurred with minimal energy use. Furthermore, the hydrochar exhibited its highest heating value at 200 °C for 4 h (HTC_200_4) which was 1.44 times higher than the raw dung (13.4 MJ/kg) due to the HTC process. The produced hydrochar demonstrated a significant improvement compared to the conventional solvent, i.e. water.

A review on hydrothermal carbonization of potential biomass wastes, characterization and environmental applications of hydrochar, and biorefinery perspectives of the process

It is imperative to search for appropriate processes to convert wastes into energy, chemicals, and materials to establish a circular bio-economy toward sustainable development. Concerning waste biomass valorization, hydrothermal carbonization (HTC) is a promising route given its advantages over other thermochemical processes. From that perspective, this article reviewed the HTC of potential biomass wastes, the characterization and environmental utilization of hydrochar, and the biorefinery potential of this process. Crop and forestry residues and sewage sludge are two categories of biomass wastes (lignocellulosic and non-lignocellulosic, respectively) readily available for HTC or even co-hydrothermal carbonization (Co-HTC). The temperature, reaction time, and solid-to-liquid ratio utilized in HTC/Co-HTC of those biomass wastes were reported to range from 140 to 370 °C, 0.05 to 48 h, and 1/47 to 1/1, respectively, providing hydrochar yields of up to 94 % according to the process conditions. Hydrochar characterization by different techniques to determine its physicochemical properties is crucial to defining the best applications for this material. In the environmental field, hydrochar might be suitable for removing pollutants from aqueous systems, ameliorating soils, adsorbing atmospheric pollutants, working as an energy carrier, and performing carbon sequestration. But this material could also be employed in other areas (e.g., catalysis). Regarding the effluent from HTC/Co-HTC, this byproduct has the potential for serving as feedstock in other processes, such as anaerobic digestion and microalgae cultivation. These opportunities have aroused the industry interest in HTC since 2010, and the number of industrial-scale HTC plants and patent document applications has increased. The hydrochar patents are concentrated in China (77.6 %), the United States (10.6 %), the Republic of Korea (3.5 %), and Germany (3.5 %). Therefore, considering the possibilities of converting their product (hydrochar) and byproduct (effluent) into energy, chemicals, and materials, HTC or Co-HTC could work as the first step of a biorefinery. And this approach would completely agree with circular bioeconomy principles.

Deactivation and Regeneration of Nitrogen Doped Carbon Catalyst for Acetylene Hydrochlorination

The poor stability of carbon materials doped with nitrogen limited their development in acetylene hydrochlorination. Therefore, investigating the deactivation reasons of carbon catalysts and researching regeneration methods became the research focus. Herein, carbon-nitrogen materials were synthesized by one-step pyrolysis, which using biomass materials with high nitrogen content, the synthesized material was used in an acetylene hydrochlorination reaction. The acetylene conversion rate of D-GH-800 catalyst was up to 99%, but the catalytic activity decreased by 30% after 60 h reaction. Thermogravimetric analysis results showed that the coke content was 5.87%, resulting in catalyst deactivation. Temperature-programmed desorption verified that the deactivation was due to the strong adsorption and difficult desorption of acetylene by the D-GH-800 catalyst, resulting in the accumulation of acetylene on the catalyst surface to form carbon polymers and leading to the pore blockage phenomenon. Furthermore, based on the catalyst deactivation by carbon accumulation, we proposed a new idea of regeneration by ZnCl₂ activation to eliminate carbon deposition in the pores of the deactivated catalyst. As a result, the activity of D-GH-800 was recovered, and lifetime was also extended. Our strategy illustrated the mechanism of carbon deposition, and the recoverability of the catalyst has promising applications.

Degradation of organic pollutants from water by biochar-assisted advanced oxidation processes: Mechanisms and applications

Biochar has shown large potential in environmental remediation because of its low cost, large specific surface area, porosity, and high conductivity. Biochar-assisted advanced oxidation processes (BC-AOPs) have recently attracted increasing attention to the remediation of organic pollutants from water. However, the effects of biochar properties on catalytic performance need to be further explored. There are still controversial and knowledge gaps in the reaction mechanisms of BC-AOPs, and regeneration methods of biochar catalysts are lacking. Therefore, it is necessary to systematically review the latest research progress of BC-AOPs in the treatment of organic pollutants in water. In this review, first of all, the effects of biochar properties on catalytic activity are summarized. The biochar properties can be optimized by changing the feedstocks, preparation conditions, and modification methods. Secondly, the catalytic active sites and degradation mechanisms are explored in different BC-AOPs. Different influencing factors on the degradation process are analyzed. Then, the applications of BC-AOPs in environmental remediation and regeneration methods of different biochar catalysts are summarized. Finally, the development prospects and challenges of biochar catalysts in environmental remediation are put forward, and some suggestions for future development are proposed.

Triazole-functionalized hydrochar-stabilized Pd nanocatalyst for ullmann coupling

Biomass valorization is essential, particularly in emerging countries. Here, hydrochar from arabica coffee straw was functionalized with a triazole group (HD-TRz) for use as a support of palladium nanoparticles (PdNPs-HD-TRz) applied in the Ullmann coupling reaction for the first time. It provided remarkably excellent selectivities, conversions at a temperature as low as 45 °C and catalyst recyclability, surpassing previous literature performances. Hydrochar was obtained by one-pot reaction via hydrothermal synthesis, using NaOH solution as activating agent and functionalized with a 1,3-triazole group by CuAAC "click" reaction. The PdNPs were prepared via reduction of hydrochar-bound Pd(II) using NaBH₄. Hydrochar functionalization was monitored by infrared spectroscopy, and X-ray diffraction (XRD) allowed to observe carbon and palladium planes in hydrochar and PdNPs HD-TRz structures. The PdNPs presented a spherical shape with 2.1 ± 0.1 nm size, homogeneously distributed in the carbon coverslips. The HD-TRz-supported PdNPs were used as a catalyst in the Ullmann reaction of iodobenzene, using ethanol as solvent with 100% of conversion and 91% selectivity at 45 °C. The material was reused, presenting 100% of conversion and selectivities of 92, 84 and 73% for the 1st, 2nd and 3rd cycle, respectively. The scope of the reaction was expanded to other molecules showing the potential of this and other triazole-hydrochar-supported nanocatalysts.

Recent advances in biochar technology for textile dyes wastewater remediation: A review

With the continuous rise of industrialization and agriculture, the concentration of organic contaminants such as dyes in the ecosystem has increased in subsequent years, causing major environmental contamination. Adsorption has been revealed to be a reliable and cost-effective way of eliminating organic pollutants. Biochar technology has the potential of converting trash into treasure when utilized for environmental remediation since it has numerous benefits such as the availability of diverse types of raw materials, low cost, and reusability. The potential of biochar as an adsorbent, support for catalysis, and a composite catalyst for dye degradation and mineralization is summarized in this research. It discusses its current research status in the adsorption and degradation of various dyes, incorporates the pertinent adsorption variables, encapsulates its regeneration techniques, investigates its engineering applications, and finally analyses limitations and discusses future development prospects.

Microwave-Assisted Hydrothermal Carbonization of Pomegranate Peels into Hydrochar for Environmental Applications

Several studies have reported that the hydrothermal carbonization method (HTC) of agricultural waste is able to produce a solid residue with interesting properties for the adsorption of organic pollutants from contaminated water. This work represents a facile method to prepare hydrochar (HC) from pomegranate peels’ waste using the microwave-assisted hydrothermal carbonization method (MHTC) at 200 °C for 1 h with a mass ratio of peel to water = 1:10. Activated hydrochar (AHC) was prepared by in situ chemical activation using ZnCl2 and MHTC. Several techniques have been applied to characterize the prepared samples as FTIR, XRD, TEM and SEM. The samples were investigated for their possible use as adsorbents of methylene blue (MB) dye. The results confirm the formation of amorphous hydrochar with a porous structure. The pH of zero point charge (pHzpc) is 4.3 and 4.6 for HC and AHC samples, respectively. The maximum adsorption capacity of HC and AHC samples are 194.9 and 12.55 mg/g (i.e., mg of adsorbate/g of adsorbent), respectively.

Highly efficient conversion of sunflower stalk-hydrolysate to furfural by sunflower stalk residue-derived carbonaceous solid acid in deep eutectic solvent/organic solvent system

Sunflower stalk was utilized as a source of raw material and catalyst for furfural production, and efficient conversion of xylose-rich hydrolysate into furfural was developed in an aqueous deep eutectic solvent/organic solvent medium by carbonaceous solid acid catalyst SO₄^2-/SnO₂-SSXR. The structural characteristics of SO₄^2-/SnO₂-SSXR was characterized by Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM), Fourier-transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Pyridine Adsorption Fourier-transform Infrared (Py-IR) and Raman. Under the optimum catalytic conditions, furfural (110.1 mM) yield reached 82.6% in a ChCl-MAA/toluene medium at 180 °C in 15 min by 3.6 wt% SO₄^2-/SnO₂-SSXR. Additionally, quite importantly, SO₄^2-/SnO₂-SSXR, ChCl-MAA and toluene had good recyclability for furfural production. The potential catalytic path of xylose dehydration into furfural was proposed by co-catalysis with SO₄^2-/SnO₂-SSXR and ChCl-MAA. This study revealed high potential sustainable application of furfural production.

Removal of Reactive Black 5 Dye by Banana Peel Biochar and Evaluation of Its Phytotoxicity on Tomato

Removal of Reactive Black 5 (RB5) dye from an aqueous solution was studied by its adsorption on banana peel biochars (BPBs). The factors affecting RB5 dye adsorption such as pH, exposure time, RB5 dye concentration, adsorbent dose, particle size and temperature were investigated. Maximum 97% RB5 dye removal was obtained at pH 3 with 75 mg/L adsorbate concentration by banana peel biochars. Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) were used to characterize the adsorbent material. The data of equilibrium were analyzed by Langmuir and Freundlich isotherm models. The experimental results were best reflected by Langmuir isotherm with maximum 7.58 mg/g adsorption capacity. Kinetic parameters were explored and pseudo-second order was found suitable which reflected that rate of adsorption was controlled by physisorption. Thermodynamic variables exhibited that the sorption process was feasible, spontaneous, and exothermic in nature. Banana peel biochar showed excellent regeneration efficiency up to five cycles of successive adsorption-desorption. Banana peel biochar maintained >38% sorption potential of RB5 dye even after five cycles of adsorption-desorption. The phytotoxic study exhibited the benign nature of BPB-treated RB5 dye on tomato seeds.

Simultaneous co-hydrothermal carbonization and chemical activation of food wastes to develop hydrochar for aquatic environmental remediation

Locally generated food wastes, such as Arabic coffee ground (ACG) and olive oil cake (OOC) were converted to N-ACG: OOC - 3 hydrochar (HC) through simultaneous co-hydrothermal carbonization (Co-HTC) and chemical activation. The optimized ACG: OOC mass ratio (g: g) and chemical activation agent used were 1.2: 0.8 and 0.1 M HNO₃, respectively. Spectroscopic analyses confirmed the dominance of oxygen-containing functionalities, whereas the X-ray diffraction pattern displayed peaks for both sucrose and cellulose on N-ACG: OOC - 3. The developed HC was tested for methylene blue (MB) and crystal violet (CV) adsorption in aqueous systems. Batch scale adsorption studies showed pH, initial concentration (C_o), time (t), and temperature (T) dependent dye uptake. Maximum dye uptake was observed at pH 7, with 50 - 70% and 76 - 90 % CV and MB removal achieved within 15 min at varied C_o: 50 - 200 mg/L. Adsorption was governed by multiple mechanisms, including hydrogen bonding, electrostatic interactions, π-π interactions, and n-π interactions. Dye elution was higher in ethanol (EtOH: C₂H₅OH), and CV elution (50.8%) was more significant than MB elution (14.8%).

Porous ZnCl2-Activated Carbon from Shaddock Peel: Methylene Blue Adsorption Behavior

It is of great interest and importance to resource utilization of waste biomass to produce porous carbon for environmental treatments. Pore structure and properties of the obtained carbon mainly relate to carbonization conditions and biomass types. In this work, a series of porous, biomass-activated carbons (AC) were prepared using shaddock peel, with ZnCl2 as a pore-forming agent. The effect of carbonization temperature and the mass ratio between ZnCl2 and shaddock peel were thoroughly investigated. The material composition, surface chemical properties, and surface structures of samples were carefully characterized. The specific surface area and adsorption capacity to methylene blue (MB) of adsorbents were changed with the carbonization temperature and the mass ratios between ZnCl2 and shaddock peel; when the temperature was at 1000 °C and the mass ratio was equal to 2:1, the resulting adsorbent had the largest specific surface area of 2398.74 m2/g and average pore size of 3.04 nm, which showed the highest adsorption capacity to MB to be 869.57 mg/g. The adsorption processes of biomass AC adsorbent matched the pseudo-second-order kinetic model and Langmuir isotherm model. This efficient and environmentally friendly biomass AC adsorbent from shaddock peel, activated by ZnCl2, is a promising candidate for the treatment of water pollution.

Structural, inorganic, and adsorptive properties of hydrochars obtained by hydrothermal carbonization of coffee waste

The hydrothermal carbonization process is a suitable process for the conversion of potentially harmful lignocellulosic waste into hydrochars. Defective coffee beans were the precursor raw material for hydrochar synthesis. Reactions were performed in a high-pressure reactor at 150, 200, and 250 °C, in autogenous pressure, for 40 min. Hydrochars were recovered by filtration and characterized by energy dispersive X-ray fluorescence spectroscopy, UV-Vis spectrophotometry, attenuated total reflection Fourier-transform infrared spectroscopy, differential thermal analysis, and scanning electron microscopy. Methylene blue adsorption tests were performed and analyzed by Langmuir and Freundlich adsorption isotherms. Adsorption mechanisms were investigated by computational calculations at DFT level. Results suggest that hydrochars from defective coffee beans can be applied as technological resources in the agronomic and environmental fields due to their inorganic composition, mainly to high magnesium content, the structural characteristics of porosity, biodegradation control, soil carbon-fixation and adsorption capacity. Important adsorption processes are caused by the development of oxygenated functional groups on the hydrochar surface.

Efficient adsorption of methylene blue on carboxylate-rich hydrochar prepared by one-step hydrothermal carbonization of bamboo and acrylic acid with ammonium persulphate

Hydrochar (AAHC) with rich carboxylate groups was prepared by one-step hydrothermal carbonization (HTC) of bamboo and acrylic acid with the presence of ammonium persulphate, and then activated by a sodium hydroxide solution. AAHC was featured by elemental analysis, SEM, XPS, FTIR, Zeta potential analysis and N₂ adsorption-desorption isotherms, and applied to test adsorptive ability of methylene blue (MB) by batch sorption experiments. Despite a small Brunauer-Emmett-Teller (BET) surface area of 5.03 m²·g^-1, AAHC has excellent MB adsorbing capacity owing to the richness of carboxylate groups. Compared with hydrochar produced without adding ammonium persulphate, AAHC exhibits larger BET surface, pore volume and carboxylate groups, indicating a small amount of ammonium persulfate plays an important role in HTC in addition to the free radical initiator. This work provides a facile and cheap method combining HTC and polymerization for preparation of carboxylate-rich hydrochar.

Efficient removal of methylene blue by activated hydrochar prepared by hydrothermal carbonization and NaOH activation of sugarcane bagasse and phosphoric acid

Activated-hydrochar (AHC) derived from sugarcane bagasse was synthesized by hydrothermal carbonization (HTC) using phosphoric acid and sodium hydroxide (NaOH) as activators. The properties of AHC were systematically characterized by elemental analysis, BET, SEM, FTIR, XPS and zeta potential, and applied to evaluate the adsorption ability of methylene blue (MB) by batch adsorption tests. The MB adsorption isotherm and kinetics of AHC were well described by the Langmuir model and pseudo-second-order kinetic model. Characteristic analysis suggested electrostatic attraction, hydrogen bonding and π-π interactions were the main contributors to MB adsorption. Analysis of mass transfer mechanisms demonstrated the adsorption process towards MB by AHC involved intra-particle diffusion to some extent. Thermodynamic studies indicated MB adsorption was an endothermic, spontaneous process associated with a disorder increase at the solid-liquid interface. The maximum adsorption capacity of AHC for MB was 357.14 mg g-1 at 303 K. Thus, the combination of HTC in phosphoric acid and NaOH activation offered a facile, green and economical alternative for conversion of sugarcane bagasse into efficient adsorbents used in wastewater treatment.

Biomass as source for hydrochar and biochar production to recover phosphates from wastewater: A review on challenges, commercialization, and future perspectives

Excessive phosphate run-off with total phosphorus concentration greater than 20 μg P L^-1 triggers the growth of harmful algal species in waterbodies and potentially leads to eutrophication. This has severe negative implications on aquatic environment and impacts human health. The annual economic impact of harmful algal blooms is reported to be as high as $25 million for public health and commercial fishery sector, $29 million for recreation/tourism sector and $2 million for monitoring and management. Adsorption is widely considered as an effective and economic strategy to achieve extremely low concentration of phosphorus. The char produced by valorizing various waste biomasses have been gaining attention in phosphorus remediation owing to their availability, their ability to regenerate and reuse. This review paper exclusively focuses on utilizing hydrochar and biochar synthesized from waste biomass, respectively, through hydrothermal carbonization and slow pyrolysis to mitigate phosphorus concentration and potential strategies for handling the spent char. The key mechanisms involved in phosphate adsorption are electrostatic interaction, ion exchange and complexation. The maximum adsorption capacity of hydrochar and biochar ranges from 14-386 mg g^-1 and 3-887 mg g^-1, respectively. Hydrochar and biochar are cost-effective alternative to commercial activated carbon and spent char can be used for multiple adsorption cycles. Furthermore, extensive research studies on optimizing the feedstock, reaction and activation conditions coupled with technoeconomic analysis and life cycle assessment could pave way for commercialization of char-based adsorption technology.

Characterization of Bio-Adsorbents Produced by Hydrothermal Carbonization of Corn Stover: Application on the Adsorption of Acetic Acid from Aqueous Solutions

In this work, the influence of temperature on textural, morphological, and crystalline characterization of bio-adsorbents produced by hydrothermal carbonization (HTC) of corn stover was systematically investigated. HTC was conducted at 175, 200, 225, and 250 °C, 240 min, heating rate of 2.0 °C/min, and biomass-to-H2O proportion of 1:10, using a reactor of 18.927 L. The textural, morphological, crystalline, and elemental characterization of hydro-chars was analyzed by TG/DTG/DTA, SEM, EDX, XRD, BET, and elemental analysis. With increasing process temperature, the carbon content increased and that of oxygen and hydrogen diminished, as indicated by elemental analysis (C, N, H, and S). TG/DTG analysis showed that higher temperatures favor the thermal stability of hydro-chars. The hydro-char obtained at 250 °C presented the highest thermal stability. SEM images of hydro-chars obtained at 175 and 200 °C indicated a rigid and well-organized fiber structure, demonstrating that temperature had almost no effect on the biomass structure. On the other hand, SEM images of hydro-chars obtained at 225 and 250 °C indicated that hydro-char structure consists of agglomerated micro-spheres and heterogeneous structures with nonuniform geometry (fragmentation), indicating that cellulose and hemi-cellulose were decomposed. EDX analysis showed that carbon content of hydro-chars increases and that of oxygen diminish, as process temperature increases. The diffractograms (XRD) identified the occurrence of peaks of higher intensity of graphite (C) as the temperature increased, as well as a decrease of peaks intensity for crystalline cellulose, demonstrating that higher temperatures favor the formation of crystalline-phase graphite (C). The BET analysis showed 4.35 m2/g surface area, pore volume of 0.0186 cm3/g, and average pore width of 17.08 μm. The solid phase product (bio-adsorbent) obtained by hydrothermal processing of corn stover at 250 °C, 240 min, and biomass/H2O proportion of 1:10, was activated chemically with 2.0 M NaOH and 2.0 M HCl solutions to investigate the adsorption of CH3COOH. The influence of initial acetic acid concentrations (1.0, 2.0, 3.0, and 4.0 mg/mL) was investigated. The kinetics of adsorption were investigated at different times (30, 60, 120, 240, 480, and 960 s). The adsorption isotherms showed that chemically activated hydro-chars were able to recover acetic acid from aqueous solutions. In addition, activation of hydro-char with NaOH was more effective than that with HCl.

Nano-activated carbon derived from date palm coir waste for efficient sequestration of noxious 2,4-dichlorophenoxyacetic acid herbicide

Alarming water contamination rates by toxic herbicides have drawn attention to treat these pollutants using efficient, easy, and economic techniques. In this work, date-palm coir (DPC) waste-based nano-activated carbon (DPC-AC) was successfully prepared and examined for adsorptive removal of toxic 2,4-dichlorophenoxyacetic acid (2,4-DPA) herbicide from synthetic wastewater. The DPC-AC was synthesized via a single-step carbonization-KOH activation approach. The nanosorbent displayed a flaky morphology with graphitic structure and oxygen-rich surface functionalities. The nanocarbon with a mean particle size of 163 nm possessed a high specific surface area of 947 m²/g with an average pore size of 2.28 nm. High 2,4-DPA removal efficiency of 98.6% was obtained for the optimal adsorption conditions of pH 2, dosage 0.15 g, rotational speed 100 rpm, time 90 min, and initial 2,4-DPA concentration of 100 mg/L. Langmuir isotherm best described the equilibrium behavior with a theoretical maximum of 50.25 mg/g adsorption capacity for the system. Pseudo-second order model was more appropriate in quantifying the kinetics for all initial feed concentrations. Thermodynamically, the adsorption process was spontaneous, endothermic, and involved low activation energy. A plausible mechanism for the adsorption-desorption of 2,4-DPA onto DPC-AC is also discussed. Cost analysis and regenerability studies proved the economic value ($3/kg) and reusable nature of DPC-AC without any significant loss in its performance. Overall, this study highlights the advantages of DPC waste valorization into efficient nanoadsorbent and the sequestration of noxious 2,4-DPA herbicide from its aqueous streams using this nanosorbent.

Hydrothermal carbonization of distillers grains with clay minerals for enhanced adsorption of phosphate and methylene blue

A novel one-pot synthesis method was developed to prepare modified hydrochar by co-hydrothermal carbonization of waste distillers grains using low-cost clay minerals (attapulgite or vermiculite). The loading of the clay minerals onto hydrochar surfaces altered the structure and surface composition of the hydrochar such that the clay-modified hydrochars showed better ability to adsorb methylene blue and phosphate in aqueous solution than the pristine hydrochar. The maximum methylene blue and phosphate adsorption capacities of the modified hydrochar reached 340.3 and 96.9 mg g^-1, respectively, comparable or higher than that of many commercial sorbents. Multiple mechanisms, including electrostatic attraction, ion exchange, complexation, and physical adsorption, controlled the adsorption process. These results highlight excellent potential for distillers grains-derived hydrochar-clay composites as an environmental sorbent, capable of removing a variety of contaminants from aqueous solutions.

Efficient Adsorption of Methylene Blue by Porous Biochar Derived from Soybean Dreg Using a One-Pot Synthesis Method

Soybean dreg is a by-product of soybean products production, with a large consumption in China. Low utilization value leads to random discarding, which is one of the important sources of urban pollution. In this work, porous biochar was synthesized using a one-pot method and potassium bicarbonate (KHCO3) with low-cost soybean dreg (SD) powder as the carbon precursor to investigating the adsorption of methylene blue (MB). The prepared samples were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental analyzer (EA), Brunauer-Emmett-Teller (BET), X-ray diffractometer (XRD), Raman spectroscopy (Raman), Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). The obtained SDB-K-3 showed a high specific surface area of 1620 m2 g-1, a large pore volume of 0.7509 cm3 g-1, and an average pore diameter of 1.859 nm. The results indicated that the maximum adsorption capacity of SDB-K-3 to MB could reach 1273.51 mg g-1 at 318 K. The kinetic data were most consistent with the pseudo-second-order model and the adsorption behavior was more suitable for the Langmuir isotherm equation. This study demonstrated that the porous biochar adsorbent can be prepared from soybean dreg by high value utilization, and it could hold significant potential for dye wastewater treatment in the future.

Removal of aqueous Cr(VI) by Zn- and Al-modified hydrochar

Pristine hydrochar is a carbonaceous material that can sorb hexavalent chromium (Cr(VI)), a kind of toxic pollutants and difficult to removal, from aqueous solution but its capacity is limited. With the goal of improving this ability, two modified hydrochars were produced by co-hydrothermal carbonization (200 °C, 7h) of bamboo sawdust with zinc chloride (ZnCl₂) or aluminum chloride (AlCl₃). Compared to the pristine hydrochar, the ZnCl₂-and AlCl₃-modified hydrochars were more fully carbonized (higher C content and lower H/C) and had higher surface area (increased by 26 and 4.3 times, respectively) and larger pore volume (increased by 43 and 5.5 times, respectively). Due to these improved properties, the Cr(VI) maximum adsorption capacity (modeled via Langmuir isotherms) of ZnCl₂-and AlCl₃-modified hydrochar increased by 3.4 and 2.8 times, respectively. In addition, Cr(VI) adsorption kinetic of modified hydrochar was well fitted by the pseudo-second-order model. Cr sorption capacity increased at low pH and ion strengths, suggesting the potential roles of electrostatic interaction and ion exchange mechanisms. These results indicate that hydrochars modified by ZnCl₂ and AlCl₃ treatment are promising in environmental applications that require Cr(VI) removal.

Novel oxone treated hydrochar for the removal of Pb(II) and methylene blue (MB) dye from aqueous solutions

This study represents the first ever work on a novel oxone treated hydrochar as an adsorbent for the efficient removal of different contaminants from aqueous solutions. Pine wood hydrochar (HC) was prepared by hydrothermal treatment at 300 °C and oxidized with oxone to produce oxidized pine wood hydrochar (OHC). Different analytical tools such as elemental analysis, FTIR, TGA, FE-SEM, and BET were used for the characterization of the OHC. Conductometric titration of OHC showed a substantial increase from 22 μmol/g to 600 μmol/g in the hydrochar carboxylic content. The OHC sorption performance was assessed by using Pb(II) ions and methylene blue (MB) dye as two models of contaminants. Sorption benchmarks were performed by varying the contaminant initial concentration, time, and temperatures. Sorption kinetic data was fitted well to the pseudo-second order kinetic model with high correlation coefficients (R² > 0.99) and isothermal data was fitted to the Langmuir model. The highest adsorption capacities for MB and Pb(II) were 86.7 mg/g and 46.7 mg/g, respectively. This study proves that oxone treatment could be a potential sustainable oxidation method to tune the hydrochar surface to increase selectivity towards heavy metal ions and dye sorption.