Green Carbon Material for Organic Contaminants Adsorption

Application of molten salt thermoelectric effect in biomass preparation of hydrogen-rich gas, porous biochar and molten salt regeneration

Hydrogen production from biomass pyrolysis is attractive since it allows for green hydrogen production through feedstock and thermal conversion. However, the key limiting factors for hydrogen production are the high oxygen content, uneven heating of biomass pellets during the slow heating process, and insufficient depolymerization due to low reaction temperatures (low gas yields and low hydrogen content). To address these challenges, fast pyrolysis of super Arundo in NaOH-Na2CO3 molten salt was carried out in this paper at 450 °C, 550 °C and 650 °C. Considering the sustainable operation and environmental problems caused by the consumption of molten salt, electrochemical electrolysis was proposed to regenerate the molten salt. The experimental results show that at 650 °C, the thermal conversion of biomass in the alkaline molten salt can prepare abundant hydrogen and simultaneously capture CO2 in situ. Compared to conventional (salt-free) pyrolysis, the percentage of H2 pyrolysis in molten salt increased from 13.11 % to 81.53 %, while CO2 decreased from 28.68 % to 2.07 %. It is noted that the mass of H in the gas exceeds the amount of H in the biomass by a factor of 1.67. This indicates that the molten salt was involved in the biomass conversion. Besides, the pyrolyzed carbon (PC) prepared in this molten salt pyrolysis system has a high specific surface area (1960.07m2/g) with many hydroxyl functional groups. Some carbon material is also produced during electrochemical molten salt regeneration, resulting from CO32- generated from the C component (C, CO, CO2) entering the molten salt and re-separated to form OH- and C. Experimental results exhibit that the regeneration ratio of NaOH reaches 24.76 %. The coupling of molten salt thermochemistry and electrochemistry realized carbon-negative utilization of low-carbon resources, this study provides practical guidance for the continuous application of molten salt including regeneration/recycling of molten salt and high-value utilization of waste molten salt.

Enhanced tribocatalytic degradation performance of organic pollutants by Cu1.8S/CuCo2S4 p-n junction

Tribocatalysis research, leveraging the triboelectric effect, presents significant potential for environmental water pollution control. However, there is a notable scarcity of studies pertaining to tribocatalysis involving heterojunctions, particularly in the context of p-n junction tribocatalysis. In this study, we employed a one-step solvothermal method to synthesize a Cu1.8S/CuCo2S4 p-n junction composite catalyst. Subsequently, we explored the tribocatalytic degradation performance of organic pollutants facilitated by the Cu1.8S/CuCo2S4 catalyst. The findings reveal that, under simple magnetic stirring conditions, the degradation rates achieved by the Cu1.8S/CuCo2S4 catalyst for tetracycline (TC), methylene blue (MB), and methyl orange (MO) are remarkably high, reaching 99.9 %, 99.7 %, and 94.0 %, respectively. This underscores the broad applicability of the Cu1.8S/CuCo2S4 catalyst for the tribocatalytic degradation of diverse organic pollutants. Experimental evidence establishes that friction occurring between the polytetrafluoroethylene (PTFE) magnet rod, the beaker, and the catalyst induces charge transfer at their interfaces, generating highly oxidized active species that effectively decompose pollutants. Through free radical capture and electron spin resonance (ESR) tests, it was empirically determined and validated that the principal active species involved in tribocatalytic degradation are holes (h+) and superoxide radicals (O2-). Incorporating insights from the experimental characterization of p-n junctions and density functional theory (DFT) theoretical calculations, we propose a plausible tribocatalytic mechanism for Cu1.8S/CuCo2S4. This research not only contributes novel findings but also serves as a reference for the exploration of innovative heterojunction tribocatalysts.

Rapid and efficient removal of multiple aqueous pesticides by one-step construction boric acid modified biochar

Tricyclazole, propiconazole, imidacloprid, and thiamethoxam are commonly used pesticides in paddy fields. It is necessary and practical to remove pesticides from the water environment because the low utilization rate of pesticides will produce residues in the water environment. It is known that there are few studies on the preparation of biochar adsorption pesticides by the walnut shell and few studies on the removal of tricyclazole and propiconazole. Based on this, this paper used the walnut shell as raw material and boric acid as an activator to prepare biochar by the one-step method. The boric acid modified walnut shell biochar (WAB4) with a specific surface area of 640.6 m2 g-1, exhibited the high adsorption capacity of all four pesticides (>70%) at pH 3-9. The adsorption capacities of tricyclazole, propiconazole, imidacloprid, and thiamethoxam were 171.67, 112.27, 156.40, and 137.46 mg g-1, respectively. The adsorption kinetics fitted the pseudo-second-order kinetic model and the adsorption isotherm curves conformed to the Freundlich isotherm model. The adsorption of pesticides by WAB4 was associated with hydrogen bonding, pore filling, hydrophobic effects, and π-π interactions. More significantly, WAB4 has excellent adsorption capacity compared to other adsorbents for real water samples. Finally, walnut shell biochar has no significant acute toxicity to Daphnia magna. This work shows that walnut shell-based biochar has a good effect on the removal of pesticides at a wide range of pH and is economical and safe, providing a new idea for the removal of pesticides in water.

Properties and the Application of Sludge-Based Biochar in the Removal of Phosphate and Methylene Blue from Water: Effects of Acid Treating

Sludge-based biochar could be used to remove phosphate and methylene blue (MB) from water. It is a highly efficient way to treat the sludge and contaminated water synergistically. The high ash content in sludge greatly influenced the adsorption property of the resultant biochar. In this work, the influence of carbonization-activation and acid treating on the adsorption performance of the sludge-based biochar was evaluated. The composition, structure, and surface properties of biochar were improved after acid treating. The biochar was obtained in a sequence of carbonization-activation first and then acid treating, providing the optimal adsorption property. Zn550-H and Zn750-H showed excellent adsorption capacity to phosphate and MB, respectively. The adsorption process was well described by the pseudo-first-order and pseudo-second-order kinetic models. Isothermal studies implied that it was controlled by multiple processes. What is more, sludge-based biochar performed well in the adsorption of phosphate and MB from weakly acidic to alkaline conditions, which was beneficial to utilize the sludge-based biochar in water remediation practically.

Effective adsorption of bisphenol A from aqueous solution over a novel mesoporous carbonized material based on spent bleaching earth

In this study, the novel mesoporous carbonized material (HSBE/C) was prepared from clay/carbon composite (SBE/C) treated with hydrofluoric acid (HF) for the first time, and was employed to efficiently adsorb bisphenol A (BPA) in water. Specifically, SBE/C was derived from the pyrolysis of spent bleaching earth (SBE), an industrial waste. HF removed SiO₂ from SBE/C and increased the specific surface area of HSBE/C (from 100.21 to 183.56 m²/g), greatly providing more adsorption sites for enhanced BPA adsorption capacity. The Langmuir monolayer maximum adsorption capacity of HSBE/C (103.32 mg/g) was much higher than the commercial activated carbon (AC) (42.53 mg/g). The adsorption process by HSBE/C followed well with the Freundlich isotherm model and the pseudo-second-order kinetic model and also was endothermic (ΔH⁰ > 0) and spontaneous (ΔG⁰ < 0). Based on the systematic characterization and factor experiment (temperature, dosage, initial pH, co-existing ions), BPA adsorption mechanism by HSBE/C likely included the hydrogen bonding, electrostatic interaction, and hydrophobic interaction. Moreover, there was no secondary pollution during the total adsorption process. Extraordinary, HSBE/C manifested stability by NaOH desorption regeneration. This study provides a new sight for application of waste-based materials as the promising adsorbents in the treatment of endocrine disruptors.

Degradation of 2,4-DCP using persulfate and iron/E-carbon micro-electrolysis coupling system

The greenhouse gas carbon dioxide (CO₂) was converted to a novel CO₂ conversion material (electrolytic carbon, EC) by molten salt electrochemical conversion, which served as the carbon source to prepare an iron-carbon composite (Fe-EC). The composite was used to activate persulfate (PS) and degrade 2,4-dichlorophenol (2,4-DCP) in an aqueous solution. The effects of several essential operating parameters such as PS dosage and pH on 2,4-DCP degradation were investigated. The removal efficiency of 2,4-DCP (20 mg L^-1) was 97.8% in the presence of Fe-EC (50 mg L^-1) and PS (1 mmol L^-1). Moreover, the average % reaction stoichiometric efficiency (RSE) (calculated for all selected times 5-60 min) was maintained at 23.07%. Electron paramagnetic resonance (EPR), classical radical scavenging experiments, and density functional theory (DFT) calculations were integrated for a mechanistic study, which disclosed that the active species in the system were identified as SO₄^⦁-, •OH, and O₂^⦁-. Moreover, the iron-carbon micro-electrolysis/PS (ICE-PS) system had a high tolerance to a wide range of pH, which would provide theoretical guidance for the treatment of organic pollutants in practical industrial wastewater.

Adsorption Behavior of Congo Red onto Barium-Doped ZnO Nanoparticles: Correlation between Experimental Results and DFT Calculations

Ba-loaded ZnO nanoparticles (Ba/ZnO) were obtained by the co-precipitation process and employed as a sorbent for Congo Red (C₃₂H₂₂N₆Na₂O₆S₂) dye (CR). Physicochemical parameters such as particle size, pH, and contact time were checked to characterize the adsorption process. The maximum adsorption capacity of Ba/ZnO NPs for CR (1614.26 mg/g) proves its potential utility in the elimination of CR dye from wastewater. The adsorption mechanism was studied via infrared spectroscopy and density functional theory calculations. The geometrical parameters and electronic properties of the CR-Ba/ZnO complex, particularly the interaction energy, the density of states, and the charge transfer, highlighted the Ba-ion mediation in the chemical bond formation between CR and the surface. The interaction between CR and Ba-doped ZnO has found to show strong chemisorption with charge transfer between the SO₃^- group and adsorbed Ba²⁺ ion on the surface.

Effectively removing tetracycline from water by nanoarchitectured carbons derived from CO2: Structure and surface chemistry influence

Understanding of the correlation between physico-chemical property of adsorbent and the adsorption performance of contaminant is very significant for developing high-efficient materials to remove antibiotic contamination from water. In this work, a novel kind of carbon adsorbent (EC) derived from CO₂ and activated ECs with modified structure via a facile chemical method using H₂ and KOH were prepared. The synthetic carbon materials (EC, EC-H₂, and EC-KOH) were then applied to remove tetracycline (TC). The kinetics of adsorption for these three carbon materials all well fitted the pseudo-second-order kinetic model. The experimental data of adsorption isotherm had good compatibility with Langmuir and Freundlich models (R² > 0.90), but the Temkin model was the most applicable for all adsorbents (R² > 0.98). A super-high adsorption capacity of EC-KOH obtained from Langmuir fitting was 933.56 mg g^-1, which was much higher than that of EC-H₂ (538.91 mg g^-1) and EC (423.30 mg g^-1), possibly due to its larger specific surface area (S_BET), pore volume, and specific surface chemical structure. Moreover, it was found that surface functional groups and large aperture of adsorbents had a positive effect on adsorption rate. More adsorption sites and surface functional groups of adsorbents were beneficial to enhance the adsorption affinity. These results are of great benefit to the directional control of carbon structure to increase the adsorption performance in rate, capacity, and affinity of antibiotics.

Hydroxyl modified hypercrosslinked polymers: targeting high efficient adsorption separation towards aniline

The removal of aniline from aqueous solution has a major environmental impact and attracted increasing attention in last few years.