Synthesis conditions of porous clay heterostructure (PCH) optimized for volatile organic compounds (VOC) adsorption

Reduction of Volatile Organic Compounds (VOCs) Emissions from Laundry Dry-Cleaning by an Integrated Treatment Process of Condensation and Adsorption

Volatile organic compounds (VOCs) are intermittently emitted at high concentrations (tens of thousands of ppmv) from small-scale laundry shops in urban areas, affecting the urban atmospheric environment. In this study, we suggested integrating VOC treatment processes incorporating condensation and adsorption in series to remove VOCs released from small-scale laundry dryers (laundry weighing less than 30 kg). We designed two different processes depending on regeneration modes for adsorber beds; an open-circuit flow process and a closed-loop flow process in regeneration mode. Our VOC treatment processes enable sustainable operation via the regeneration of adsorbers on a regular basis. Before applying the VOC treatment processes, average concentration of total volatile organic compounds (TVOCs) was 4099 ppmv (12,000 ppmv of the peak concentration) during the drying operation. After applying our closed-loop flow process, TVOC concentration decreased to 58 ppmv, leading to 98.5% removal efficiency. We also verified the robustness of our process performance in a continuous operation (30 cycles) by using a process simulation program. Lastly, we observed that our integrated treatment process can contribute to reductions in ozone and secondary organic aerosol generation by 90.4% and 95.9%, respectively. We concluded that our integrated VOC treatment processes are applicable to small-scale laundry shops releasing high-concentration VOCs intermittently, and are beneficial to the atmospheric environment.

An eco-environmental assessment of harmful algal bloom mitigation using modified clay

The application of modified clay (MC) to mitigate harmful algal blooms (HABs) is becoming a widespread practice in China because of its low cost, high efficiency and environmental friendliness. Due to its success in China, this technology has also gained international recognition in recent years. Nevertheless, the eco-environmental impacts of this technology still remain to be a concern to many customers and government agencies, which has motivated scientists in both China and many other countries to evaluate its potential effects on nontarget aquatic organisms, water quality and the benthic environment. This paper reviews the results from these studies both in the laboratory and in the field, which showed that MC does not harm nontarget aquatic organisms and has no negative impact on water quality or the benthic environment. Additionally, findings show that MC can alter nutrient cycling and reduce algal toxins in water bodies. Furthermore, researchers also found that MC affects cyst formation and germination in sedimentary environments. This review is expected to provide scientific guidance for mitigating HABs in China and worldwide using clay or MC.

Porous Clay Heterostructure with Alginate Encapsulation for Toluene Removal

A volatile organic compound adsorbent based on a porous clay heterostructure (PCH) with alginate biopolymer was successfully prepared. From N₂ adsorption-desorption analysis, the specific surface area, pore volume, and pore size of bentonite were dramatically increased after introducing the porous structure. Following complexation with alginate (Alg-PCH), the pore volume and pore size were not significantly affected by pore structure. The thermal stability of Alg-PCH shows enhanced thermal stability compared to alginate and alginate beads. The morphology layered structure of Alg-PCH was carried out by transmission electron microscopy (TEM), suggesting the disorder and re-order of the c-axis layer stacking by porous structure and complexation with alginate, respectively, which was well-matched with X-ray diffraction results. To optimize the preparation of Alg-PCH, various reaction conditions (alginate, CaCl₂ concentration, bead size, and weight ratio between alginate and PCH) were utilized. According to the toluene adsorption-desorption experiments, the preparation conditions for Alg-PCH were selected as a 2 mm extrusion tip, 0.5% of alginate, and 2% of CaCl₂ solution with a 1:50 alginate:PCH weight ratio. Additionally, it shows 61.63 mg/g adsorption capacity with around 49% desorption efficacy under atmospheric temperature and pressure.

Recent advances in volatile organic compounds abatement by catalysis and catalytic hybrid processes: A critical review

Air pollution, particularly for toxic and harmful compounds to humans and the environment, has aroused increasing public concerns. Among air pollutants, volatile organic compounds (VOCs) are the main sources of air pollution. Many attempts have been made to control VOCs using catalysts, plasma, photolysis, and adsorption. Among them, oxidative catalysis by noble metals or transition metal oxides is considered one of the most feasible and effective methods to control VOCs. This paper reviews the experimental achievements on the abatement of VOCs using noble metals, transition metals and modified metal oxide catalysts. Although the catalytic degradation of VOCs appears to be feasible, there are unavoidable problems when only catalysis treatments are applied to the field. Therefore, catalysts including hybrid processes are developed to improve the removal efficiency of VOCs. This review addresses new hybrid treatments to remove VOCs using catalysts, including hybrid treatment combined with plasma, photolysis, and adsorption. The mechanism of the oxidation of VOCs by catalysts is explained by adsorption-desorption principles, such as the Langmuir-Hinshelwood, Eley-Rideal, and Mars-van-Krevelen mechanisms. A π-backbonding interaction between unsaturated compounds and transition metals is introduced to better understand the mechanism of VOC removals. Finally, several factors affecting the catalytic activities, such as support, component ratio, preparation method, metal loading, and deactivation factor, are discussed.