Changes in surface characteristics and adsorption properties of 2,4,6-trichlorophenol following Fenton-like aging of biochar

Effects of Physical and Chemical Aging of Colloidal Activated Carbon on the Adsorption of Per- and Polyfluoroalkyl Substances

Colloidal activated carbon (CAC) is an injectable adsorbent that sequesters per- and polyfluoroalkyl substances (PFAS) in the subsurface, serving as an in situ remediation technology for PFAS-impacted sites. However, the effectiveness of the CAC sorptive barrier could change over time due to alterations in its physicochemical properties induced by aging processes. In this study, the effects of CAC aging on surface properties of CAC and resulting impact on the adsorption behaviors of PFAS compounds were determined using four accelerated aging treatments, including wet-dry cycling (W/D), hydrogen peroxide (H), Fenton's reagent (F), and mineral acid (A). Fenton's reagent and mineral acid aging treatments showed a greater impact on the physical structure and chemical composition of CAC than either W/D-CAC and H-CAC. Aging the CAC lowered the CAC specific surface area and anion exchange capacity, increased surface oxygen content, and lowered the point of zero charge, suggesting negative impacts on the capacity of CAC for PFAS removal. This reduction in the sorption capacity was confirmed in batch sorption isotherm experiments. All aged CAC had lower PFAS adsorption in a multisolute system, including six PFAS compounds with different chain lengths (C4-C8) and functional groups (sulfonate or carboxylate), with the only exception being perfluorooctanesulfonic acid (PFOS). The results suggest that the aging process is an important, yet often overlooked, factor in determining the long-term effectiveness of the CAC sorptive barrier for PFAS removal, especially for shorter-chain hydrophilic PFAS. More research is needed to verify the influence of field-scale aging processes on the CAC performance and longevity.

Evaluation of Fenton-like reaction for sorption and degradation of kasugamycin in the presence of biochar

Although the use of biochar as an adsorbent for the removal of various pollutants from wastewater is well established, the use of biochar/modified biochar for the scavenging of antibiotics from aqueous media in the Fenton-like system receives less attention. The highest kasugamycin (KSM) adsorption capacity (5.0 mg g-1) was obtained from the pristine biochar at the lowest initial pH of 3 in Fenton-like system. The Fenton-like system improved the KSM adsorption capacity of pristine biochar by 222.2%, 169.9%, and 159.9% at 25 °C, 35 °C, and 45 °C comparing to control, respectively, and it also increased adsorption capacity by 97.4%, 63.8%, and 56.8% comparing to modified biochar. The amounts of biochar applied and the Fenton-like system affected KSM mineralization and degradation. The KSM degradation products had a significant amount of small molecular organic matter (m/z 384) and a tetrahydropyran structure that was difficult to degrade. The highly efficient degradation of KSM in Fenton-like system can be attributed to the generation of large amounts of hydroxyl radical (·OH) and functional groups (C=C, C=O, etc.).

A systematic review of biochar aging and the potential eco-environmental risk in heavy metal contaminated soil

Biochar is widely accepted as a green and effective amendment for remediating heavy metals (HMs) contaminated soil, but its long-term efficiency and safety changes with biochar aging in fields. Currently, some reviews have qualitatively summarized biochar aging methods and mechanisms, aging-induced changes in biochar properties, and often ignored the potential eco-environmental risk during biochar aging process. Therefore, this review systematically summarizes the study methods of biochar aging, quantitatively compares the effects of different biochar aging process on its properties, and discusses the potential eco-environmental risk due to biochar aging in HMs contaminated soil. At present, various artificial aging methods (physical aging, chemical aging and biological aging) rather than natural field aging have been applied to study the changes of biochar's properties. Generally, biochar aging increases specific surface area (SSA), pore volume (PV), surface oxygen-containing functional group (OFGs) and O content, while decreases pH, ash, H, C and N content. Chemical aging method has a greater effect on the properties of biochar than other aging methods. In addition, biochar aging may lead to HMs remobilization and produce new types of pollutants, such as polycyclic aromatic hydrocarbons (PAHs), environmentally persistent free radicals (EPFRs) and colloidal/nano biochar particles, which consequently bring secondary eco-environmental risk. Finally, future research directions are suggested to establish a more accurate assessment method and model on biochar aging behavior and evaluate the environmental safety of aged biochar, in order to promote its wider application for remediating HMs contaminated soil.

Efficient roxarsone degradation by low-dose peroxymonosulfate with the activation of recycling iron-base composite material: Critical role of electron transfer

Pollutant degradation via electron transfer based on advanced oxidation processes (AOPs) provides an economical and energy-efficient method for pollution control. In this study, an iron-rich waste, heating pad waste (HPW), was recycled as a raw material, and a strong magnetic catalyst (Fe-HPW) was synthesized at high temperature (900 °C). Results showed that in the constructed Fe-HPW/PMS system, effective roxarsone (ROX) degradation and TOC removal (72.54%) were achieved at a low-dose of oxidant (PMS, 0.05 mM) and catalyst (Fe-HPW, 0.05 g L-1), the ratio of PMS to ROX was only 2.5:1. In addition, the released inorganic arsenic was effectively removed from the solution. The analysis of the experimental results showed that ROX was effectively degraded by forming PMS/catalyst surface complexes (Fe-HPW-PMS*) to mediate electron transfer in the Fe-HPW/PMS system. Besides, this system performed effective ROX degradation over a wide pH range (pH=3-9) and showed high resistance to different water parameters. Overall, this study not only provides a new direction for the recycling application of HPW but also re-emphasizes the neglected nonradical pathway in advanced oxidation processes.

Enhanced adsorption for trivalent antimony by nano-zero-valent iron-loaded biochar: performance, mechanism, and sustainability

The discharge of tailing leachate and metallurgical wastewater has led to an increasing trend of water pollution. In this study, nZVI-modified low-temperature biochar was used to adsorb Sb(III) from water. The adsorption capacity and speed of nZVI-BC were better than those of BC, and the best adsorption effect was observed for 4nZVI-BC, with 93.60 mg·g-1 maximum adsorptive capacity, which was 208.61% higher than the original BC. The Langmuir and Temkin models were well fitted (R2 ≥ 0.99), and PSO was more in line with the 4nZVI-BC adsorption process, indicating that the adsorption was a monolayer physico-chemical adsorption. The combination of XRD, FTIR, and XPS characterization demonstrated that the adsorption mechanism predominantly included redox reactions, complexation, and electrostatic interactions. The thermodynamic results demonstrated that 4nZVI-BC adsorption on Sb(III) was a spontaneous endothermic process. Additionally, the order of the influence of interfering ions on 4nZVI-BC was CO32-  > H2PO4-  > SO42-  > Cl-. After three repeated uses and adsorption-desorption, the adsorption ratio of Sb(III) by 4nZVI-BC was still as high as 90% and 65%, respectively. This study provides a theoretical reference for the exploration and development of Sb(III) removal technologies for aquatic environments.

Use of biochar co-mediated chitosan mesopores to encapsulate alkane and improve thermal properties

Phase-change materials (PCMs) plays a significant role in energy conservation and thermal management systems. However, excessive seepage and insufficient thermal conductivity of pristine PCMs are restricting its real-world applications. Herein, "anisotropic-like" biochar with favorable pore characteristics is designed by combining it with chitosan for dodecane encapsulation. The use of biochar could overcome high manufacturing costs and associated environmental issues of PCM supporting materials. Biochar co-mediated chitosan enrich the mesopore proportion (96.5%) and provide interactive synergistic architecture. The prepared composite PCM exhibited outstanding latent heat retention of 95.9% after repeated cycling, high loading ratio, enhanced thermal conductivity (0.373 W/(m·K)), leakage-free, and repeatable utilization properties above the melting point of pristine dodecane. A figure of merit of 33.94 × 10⁶ W² S/(m^4oC) was achieved, far surpassing that measure among reported biochar-based composite PCMs. This study provides insights into next-generation sustainable energy storage development for a key global sustainability goal.

Hexavalent chromium elimination from wastewater by integrated micro-electrolysis composites synthesized from red mud and rice straw via a facile one-pot method

The widely spread chromium (Cr) contamination is rising environmental concerns, while the reutilization of agro-industrial by-products are also urgently demanded due to their potential risks. In this study, we prepared the integrated micro-electrolysis composites (IMC) through a facile one-pot method with red mud and rice straw. The effects of components relatively mass ratios as well as pyrolysis temperature were analyzed. The XRD, XPS, SEM, FTIR, and various techniques proved the IMC was successfully synthesized, which was also used to analyze the reaction mechanisms. In this study, the dosage of IMC, pH, adsorption time, and temperature of adsorption processes were explored, in the adsorption experiment of Cr(VI), dosage of IMC was 2 g/L (pH 6, 25 °C, and 200 rpm) for isothermal, while the concentration and contact time were also varied. According to the batch experiments, IMC exhibited acceptable removal capacity (190.6 mg/g) on Cr(VI) and the efficiency reached 97.74%. The removal mechanisms of adsorbed Cr(VI) were mainly elaborated as chemical reduction, complexation, co-precipitation, and physical adherence. All these results shed light on the facile preparation and agro-industrial by-products recycled as engineering materials for the heavy metals decontamination in wastewater.

Understanding the Surface Characteristics of Biochar and Its Catalytic Activity for the Hydrodeoxygenation of Guaiacol

Biochar (BCR) was obtained from the pyrolysis of a palm-oil-empty fruit bunch at 773 K for 2 h and used as a catalyst for the hydrodeoxygenation (HDO) of guaiacol (GUA) as a bio-oil model compound. Brunauer–Emmet–Teller surface area analysis, NH3 and CO2-temperature-programmed desorption, scanning electron microscope–dispersive X-ray spectroscopy, CHN analysis and X-ray fluorescence spectroscopy suggested that macroporous and mesoporous structures were formed in BCR with a co-presence of hydrophilic and hydrophobic sites and acid–base behavior. A combination of infrared, Raman and inelastic neutron scattering (INS) was carried out to achieve a complete vibrational assignment of BCR. The CH–OH ratio in BCR is ~5, showing that the hydroxyl functional groups are a minority species. There was no evidence for any aromatic C–H stretch modes in the infrared, but they are clearly seen in the INS and are the majority species, with a ratio of sp3–CH:sp2–CH of 1:1.3. The hydrogen bound to sp2–C is largely present as isolated C–H bonds, rather than adjacent C–H bonds. The Raman spectrum shows the characteristic G band (ideal graphitic lattice) and three D bands (disordered graphitic lattice, amorphous carbon, and defective graphitic lattice) of sp2 carbons. Adsorbed water in BCR is present as disordered layers on the surface rather than trapped in voids in the material and could be removed easily by drying prior to catalysis. Catalytic testing demonstrated that BCR was able to catalyze the HDO of GUA, yielding phenol and cresols as the major products. Phenol was produced both from the direct demethoxylation of GUA, as well as through the demethylation pathway via the formation of catechol as the intermediate followed by deoxygenation.