Preparation of high-yield N-doped biochar from nitrogen-containing phosphate and its effective adsorption for toluene

Mechanisms of adsorption and functionalization of biochar for pesticides: A review

Agricultural production relies heavily on pesticides. However, factors like inefficient application, pesticide resistance, and environmental conditions reduce their effective utilization in agriculture. Subsequently, pesticides transfer into the soil, adversely affecting its physicochemical properties, microbial populations, and enzyme activities. Different pesticides interacting can lead to combined toxicity, posing risks to non-target organisms, biodiversity, and organism-environment interactions. Pesticide exposure may cause both acute and chronic effects on human health. Biochar, with its high specific surface area and porosity, offers numerous adsorption sites. Its stability, eco-friendliness, and superior adsorption capabilities render it an excellent choice. As a versatile material, biochar finds use in agriculture, environmental management, industry, energy, and medicine. Added to soil, biochar helps absorb or degrade pesticides in contaminated areas, enhancing soil microbial activity. Current research primarily focuses on biochar produced via direct pyrolysis for pesticide adsorption. Studies on functionalized biochar for this purpose are relatively scarce. This review examines biochar's pesticide absorption properties, its characteristics, formation mechanisms, environmental impact, and delves into adsorption mechanisms, functionalization methods, and their prospects and limitations.

The effect of the pyrolysis temperature and biomass type on the biocarbons characteristics

The conversion of biomass and natural wastes into carbon-based materials for various applications such as catalysts and energy-related materials is a fascinating and sustainable approach emerged during recent years. Precursor nature and characteristics are complex, hence, their effect on the properties of resulting materials is still unclear. In this work, we have investigated the effect of different precursors and pyrolysis temperature on the properties of produced carbon materials and their potential application as negative electrode materials in Li-ion batteries. Three biomasses, lignocellulosic brewery spent grain from a local brewery, catechol-rich lignin and tannins, were selected for investigations. We show that such end-product carbon characteristic as functional and elemental composition, porosity, specific surface area, defectiveness level, and morphology strictly depend on the precursor composition, chemical structure, and pyrolysis temperature. The electrochemical characteristics of produced carbon materials correlate with the characteristics of the produced materials. A higher pyrolysis temperature is shown to be favourable for production of carbon material for the Li-ion battery application in terms of both specific capacity and long-term cycling stability.

Adsorption of pyrolysis oil model compound (phenol) with plasma-modified hydro-chars and mechanism exploration

Phenol is one of the important ingredients of pyrolysis oil, contributing to the high biotoxicity of pyrolysis oil. To promote the degradation and conversion of phenol during anaerobic digestion, cheap hydro-chars with high phenol adsorption capacity were produced. The phenol adsorption capabilities of the plain hydro-char, plasma modified hydro-char at 25 °C (HC-NH3-P-25) and 500 °C (HC-NH3-P-500) were evaluated, and their adsorption kinetics and thermodynamics were explored. Experimental results indicate that the phenol adsorption capability of HC-NH3-P-500 was the highest. The phenol adsorption kinetics of all samples followed the pseudo-second-order equation and interparticle diffusion model, indicating that the adsorption rate of phenol was controlled by interparticle diffusion and chemistry adsorption simultaneously. By DFT calculations, π-π stacking and hydrogen bond are the main interactions for phenol adsorption. It was observed that an enriched graphite N content decreased the average vertical distance between hydro-chars and phenol in π-π stacking complex, from 3.5120 to 3.4532 Å, causing an increase in the negative adsorption energy between phenol and hydro-char from 13.9330 to 23.4181 kJ/mol. For hydrogen bond complex, the average vertical distance decreased from 3.4885 to 3.3386 Å due to the increase in graphite N content; causing the corresponding negative adsorption energy increased from 19.0233 to 19.9517 kJ/mol. Additionally, the presence of graphite N in the hydro-char created a positive diffusion region and enhanced the electron density between hydro-char and phenol. Analyses suggest that enriched graphite N contributed to the adsorption complex stability, resulting in an improved phenol adsorption capacity.

Physicochemical Properties and Application of Silica-Doped Biochar Composites as Efficient Sorbents of Copper from Tap Water

This article concerns research on new sorption materials based on silica-doped activated carbon. A two-stage synthesis involved pyrolysis of plant material impregnated in a water glass solution, followed by hydrothermal activation of the pyrolysate in KOH solution. The resulting composite can be used as a sorbent in drinking water filters. The proposed method of synthesis enables the design of materials with a surface area of approximately 150 m²·g^-1, whose chemical composition and structure were confirmed by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG/DTA) and Fourier-transform infrared spectroscopy (FTIR). The sorption properties of the obtained materials were determined relative to copper ions using the batch experiment method. The optimal operating parameters of the obtained materials relative to copper ions are T = 313.15 K, pH = 5, S:L ratio = 4 g·dm^-3 and t = 120 min. The research shows that the sorption kinetics of copper ions can be described by a pseudo-second-order model. The plotted copper(II) sorption isotherm clearly indicates the Langmuir model. Under optimal conditions, the maximum sorption of copper ions was 37.74 mg·g^-1, which is a satisfactory result and confirms the possibility of using the obtained material in drinking water filters.

One-Pot Synthesis of Rubber Seed Shell-Derived N-Doped Ultramicroporous Carbons for Efficient CO2 Adsorption

In this work, a series of novel rubber seed shell-derived N-doped ultramicroporous carbons (NPCs) were prepared by one-step high-temperature activation (500–1000 °C), using melamine as the nitrogen source and KOH as the activator. The effects of the melamine dosage and the activation temperatures on the surface chemical properties (doped N contents and N species), textural properties (surface area, pore structure, and microporosity), CO₂ adsorption capacities, and CO₂/N₂ selectivity were thoroughly investigated and characterized. These as-prepared NPCs demonstrate controllable BET surface areas (398–2163 m²/g), ultramicroporosity, and doped nitrogen contents (0.82–7.52 wt%). It was found that the ultramicroporosity and the doped nitrogens significantly affected the CO₂ adsorption and the separation performance at low pressure. Among the NPCs, highly microporous NPC-600-4 demonstrates the largest CO₂ adsorption capacity of 5.81 mmol/g (273 K, 1.0 bar) and 3.82 mmol/g (298 K, 1.0 bar), as well as a high CO₂/N₂ selectivity of 36.6, surpassing a lot of reported biomass-based porous carbons. In addition, NPC-600-4 also shows excellent thermal stability and recycle performance, indicating the competitive application potential in practical CO₂ capture. This work also presents a facile one-pot synthesis method to prepare high-performance biomass-based NPCs.

Recyclable nitrogen-doped biochar via low-temperature pyrolysis for enhanced lead(II) removal

Facile and low-cost preparation are essential in the conversation of agricultural waste into biochar. In this work, nitrogen-doped biochar (NBC-350-0.1) was prepared by thermal decomposition of urea (urea/biochar = 0.1:1 mass ratio) at a low temperature of 350 °C. NBC-350-0.1 showed good performance for Pb(II) removal with the maximum adsorption capacity of 130.87 mg g^-1 at 25 °C, which was five times that of pristine biochar (BC). Adsorption kinetics, isotherms and thermodynamics studies indicated that the adsorption of Pb(II) by NBC-350-0.1 or BC was the homogeneous monolayer adsorption with chemical action as the rate-limiting step, and was accompanied by spontaneous endothermic. Further analysis showed that the removal of Pb(II) on NBC-350-0.1 and BC depended on the complexation with unsaturated carbon bonds and ion exchange with Ca(II). Moreover, graphitic- and pyridinic-N in NBC-350-0.1 exerted a key part in the adsorption of Pb(II). NBC-350-0.1 regenerated by NaOH exhibited excellent recycling performance keeping the original removal efficiency at 84% after five cycles. In addition, this N doping method is suitable for improving the performance of coffee grounds, sawdust, and bagasse biochar. These results would provide an idea for obtaining recyclable N-doped biochar to treat the Pb(II) polluted wastewater.

Formation of nitrogen functionalities in biochar materials and their role in the mitigation of hazardous emerging organic pollutants from wastewater

Emerging organic pollutants (EOPs) are serious environmental concerns known for their prominent adverse and hazardous ecological effects, and persistence in nature. Their detrimental impacts have inspired researchers to develop the strategic tools that reduce and overcome the challenges caused by EOPs' rising concentration. As such, biochar becomes as a promising class of biomass-derived functional materials that can be used as low-cost and environmentally-friendly emerging catalysts to remove EOPs. Herein, in-depth synthetic strategies and formation mechanisms of biochar-based nitrogen functionalities during thermochemical conversion are presented. Most prominently, the factors affecting N-surface functionalities in biochar are discussed, emphasizing the most effective N-doping approach, including intrinsic N-doping from biomass feedstock and extrinsic N-doping from exogenous sources. Moreover, biochar-assisted EOPs removal in line with interactions of nitrogen functionalities and contaminants are discussed. The possible reaction mechanisms, i.e., radical and non-radical degradation, physical adsorption, Lewis acid-base interaction, and chemisorption, driven by N-functionalities, are addressed. The unresolved challenges of the potential applications of biochar-mediated functionalities for EOPs removal are emphasized and the outlooks of future research directions are proposed at the end.

Ethylbenzene and toluene interactions with biochar from municipal solid waste in single and dual systems

The present study investigated adsorptive removal of toluene and ethylbenzene from the aqueous media via using biochar derived from municipal solid waste (termed "MSW-BC") in a single and binary contaminant system at 25-45 °C. The adsorption was evaluated at different pH (3-10), experimental time (up to 24 h), and initial adsorbate concentrations (10-600 μg/L) in single and binary contaminant system. A fixed-bed column experiment was also conducted using MSW-BC (0.25%) and influent concentration of toluene and ethylbenzene (4 mg/L) at 2 mL/min of flow rate. The adsorption of toluene and ethylbenzene on the MSW-BC was mildly dependent on the pH, and the peak adsorption ability (44-47 μg/g) was recorded at a baseline pH of ~8 in mono and dual contaminant system. Langmuir and Hill are the models that match the isotherm results in a single contaminant environment for both toluene (R² of 0.97 and 0.99, respectively) and ethylbenzene (R² of 0.99 and 0.99, respectively) adsorption. In the binary system, the isotherm models matched in the order of Langmuir > Hill > Freundlich for toluene, whereas Hill > Freundlich > Langmuir for ethylbenzene. The adsorption in the batch experiment was likely to take place via cooperative and multilayer adsorption onto MSW-BC involving hydrophobic, π- π and n- π attractions, specific interaction such as hydrogen-π and cation-π interactions, and van der Waals interactions. The thermodynamic results indicate exothermic adsorption occurred by physical attractions between toluene and ethylbenzene, and MSW-BC. The breakthrough behavior of toluene and ethylbenzene was successfully described with Yoon-Nelson and Thomas models. The data demonstrate that the low-cost adsorbent derived from the municipal solid waste can be utilized to remove toluene and ethylbenzene in landfill leachate.

Air oxidation coupling NH3 treatment of biomass derived hierarchical porous biochar for enhanced toluene removal

In this study, hierarchical porous biochar was prepared from poplar sawdust by air oxidation coupling with NH₃ treatment for the removal of toluene. The results showed that the mesopore volume of the sample with air oxidation (PS‒O₂) increased significantly to 0.263 cm³/g from the blank sample (PS, 0.053 cm³/g). This could be attributed to the selective removal of the lignin carbon by air oxidation to develop mesopores in biochar. Following further NH₃ treatment (PS‒O₂‒NH₃), the basic surface chemistry on biochar was improved due to increased basic N-containing groups and decreased acidic O-containing groups, together with the micropore volume also increased to 0.231 cm³/g from 0.186 cm³/g of PS‒O₂. The formation mechanism of hierarchical porous structure of biochar was also discussed. The adsorption capacity of PS‒O₂‒NH₃ for toluene reached 218.4 mg/g at the initial concentration of 820 mg/m³, which was 383.2% higher than that of PS. The adsorption isotherm study indicated that the adsorption process of toluene was monolayered and the maximal adsorption capacity of PS‒O₂‒NH₃ for toluene could reach as high as 476.2 mg/g. The results demonstrated that air oxidation coupling NH₃ treatment is a highly effective method for the preparation of hierarchical porous biochar for enhancing toluene adsorption performance.

Contribution of nitrogen configurations to the adsorption of Cd(ii) in nitrogen-enriched biochar

Graphitic-N in a carbon framework can form cationic–π interactions with Cd(ii) to promote adsorption.

Pyrolyzed fabrication of N/P co-doped biochars from (NH4)3PO4-pretreated coffee shells and appraisement for remedying aqueous Cr(VI) contaminants

In this study, an agricultural residue-derived biochar was fabricated by pyrolyzing coffee shells using (NH₄)₃PO₄ pretreatment. The influence of pyrolysis temperature on the structure and properties of biochars was investigated. The elemental analysis, spectroscopic and textural studies showed that the biochars were endued sufficient N and P co-doping and large specific surface area by (NH₄)₃PO₄-pretreatment. The appraisement for remedying aqueous Cr(VI) contaminants demonstrated that the N/P co-doped biochars offered high efficiencies above 95% for aqueous Cr(VI) removal. The mechanism investigation displayed that the adsorption and reduction of Cr(VI) were boosted by the synergistic effect between the hierarchical pore structure and the groups related to oxygen, nitrogen and phosphorus. Moreover, the biochar can be readily regenerated by HCl solution soaking for reuses several times. This work should permit for providing a convenient utilization of coffee shell agricultural residues, and the coffee shell-derived biochars supplied potential for remedying Cr(VI) in effluents.

Urea/ZnCl2 in situ hydrothermal carbonization of Camellia sinensis waste to prepare N-doped biochar for heavy metal removal

Environmental benefits of biochar require a simple and effective method for preparation of functional N-doped biochar. In this study, urea/ZnCl₂ was developed to prepare N-doped biochar via in situ hydrothermal carbonization (HTC) of Camellia sinensis waste at 120-280 °C for 2 h under 1.0-9.8 MPa. Physicochemical and structural properties of the N-doped biochar were investigated by Raman spectra, elemental analysis, BET surface area, SEM, TEM, XRD, and XPS. The results showed that the N content in biochar could reach up to 7.79% at 280 °C. Surface chemistry suggested that pyridinic N, pyrollic N, and graphitic N were the major N species on the biochar. Moreover, the N-doped biochar was successfully employed to remove metal ions Cu²⁺, Pb²⁺, Zn²⁺, and Cr⁶⁺. Adsorption data fit closely to the pseudo-second-order kinetic equation and the Langmuir adsorption isotherm model for all metal ions.

Sorption of carbendazim on activated carbons derived from rape straw and its mechanism

Due to the production and widespread application of pesticides, pesticide pollution poses a potential danger to human health and the ecosystem. Herein, activated carbons employing rape straw as a precursor were produced using H₃PO₄ as an activating agent at various temperatures (300–600 °C). The activated carbons differed with respect to the physicochemical properties, which were derived from elemental analysis, N₂ sorption–desorption, FTIR, XPS, XRD, pH_pzc, Boehm titration and blocking of the oxygen-containing groups. The oxygen-containing functional groups and the pore structure of the activated carbons obtained from the different preparation conditions were quite different. The as-prepared samples were applied as sorbents to remove carbendazim (CBD). The results indicated that the sorption of CBD was mainly dominated by partitioning at low concentrations of CBD. Meanwhile, electrostatic attractions played a more important role than hydrophobic interactions at a low initial pH; in contrast, as the initial pH increased, the hydrophobic interaction was the predominant sorption mechanism. Therefore, the results can be used to design some efficient and environmentally friendly adsorbents to reduce the risk of organic pollutants, especially organic pesticides, in aqueous solutions.

Due to the production and widespread application of pesticides, pesticide pollution poses a potential danger to human health and the ecosystem.