Removal of volatile organic compounds (VOCs) from waste air stream using ozone assisted zinc oxide (ZnO) nanoparticles coated on zeolite

Cooperative and Bifunctional Adsorbent-Catalyst Materials for In-situ VOCs Capture-Conversion

Volatile organic compounds (VOCs) are gases that are emitted into the air from products or processes and are major components of air pollution that significantly deteriorate air quality and seriously affect human health. Different types of metals, metal oxides, mixed-metal oxides, polymers, activated carbons, zeolites, metal-organic frameworks (MOFs) and mixed-matrixed materials have been developed and used as adsorbent or catalyst for diversified VOCs detection, removal, and destruction. In this comprehensive review, we first discuss the general classification of VOCs removal materials and processes and outline the historical development of bifunctional and cooperative adsorbent-catalyst materials for the removal of VOCs from air. Subsequently, particular attention is devoted to design of strategies for cooperative adsorbent-catalyst materials, along with detailed discussions on the latest advances on these bifunctional materials, reaction mechanisms, long-term stability, and regeneration for VOCs removal processes. Finally, challenges and future opportunities for the environmental implementation of these bifunctional materials are identified and outlined with the intent of providing insightful guidance on the design and fabrication of more efficient materials and systems for VOCs removal in the future.

Recent advancements in sustainable synthesis of zinc oxide nanoparticles using various plant extracts for environmental remediation

The sustainable synthesis of zinc oxide nanoparticles (ZnO-NPs) using plant extracts has gained significant attention in recent years due to its eco-friendly nature and potential applications in numerous fields. This synthetic approach reduces the reliance on non-renewable resources and eliminates the need for hazardous chemicals, minimizing environmental pollution and human health risks. These ZnO-NPs can be used in environmental remediation applications, such as wastewater treatment or soil remediation, effectively removing pollutants and improving overall ecosystem health. These NPs possess a high surface area and band gap of 3.2 eV, can produce both OH° (hydroxide) and O2-° (superoxide) radicals for the generation of holes (h+) and electrons (e-), resulting in oxidation and reduction of the pollutants in their valence band (VB) and conduction band (CB) resulting in degradation of dyes (95-100% degradation of MB, MO, and RhB dyes), reduction and removal of heavy metal ions (Cu2+, Pb2+, Cr6+, etc.), degradation of pharmaceutical compounds (paracetamol, urea, fluoroquinolone (ciprofloxacin)) using photocatalysis. Here, we review an overview of various plant extracts used for the green synthesis of ZnO NPs and their potential applications in environmental remediation including photocatalysis, adsorption, and heavy metal remediation. This review summarizes the most recent studies and further research perspectives to explore their applications in various fields.

Preparation and application of zeolite-zinc oxide nano composite for nitrate removal from groundwater

Nanomaterial assisted removal of pollutants from water has got great attention. This study aimed to remove nitrate from groundwater using zeolite and zeolite-ZnO nanocomposite as synergetic effect. Zeolite-ZnO nanocomposite was prepared using the co-precipitation method. The Physico-chemical characteristics of the nanomaterials were determined using XRD, SEM, and FTIR. The results revealed that; Zeolite-ZnO nanocomposites with 13.12 nm particle size have successfully been loaded into the zeolite. In addition, its chemical composition was determined using AAS. The removal efficiency of nitrate from groundwater was studied using a batch experiment. The removal of nitrate was investigated as a function of adsorbent dose, pH, initial concentration of nitrate, contact time, and agitation speed. Moreover, the adsorption isotherm and kinetics were also determined. The results showed that the removal of nitrate was 92% at an optimum dose of 0.5 g, pH 5, initial nitrate concentration of 50 mg/L, the contact time of 1 h, and agitation speed of 160 rpm. The removal nitrate has been fitted well by the Langmuir isotherm model with correlation coefficients of R² = 0.988. Thus, indicating the applicability of monolayer coverage of the nitrate ion on the surface of the nanocomposite. The adsorption process follows the pseudo-second-order model with a correlation coefficient of R² = 0.997. The results of this work might find application in remediation of water by removing nitrate to meet the standards of water quality.

Gaseous ethylbenzene removal by photocatalytic TiO2 nanoparticles immobilized on glass fiber tissue under real conditions: evaluation of reactive oxygen species contribution to the photocatalytic process

Photocatalytic oxidation (PCO) using a TiO₂ catalyst is an effective technique to remove gaseous volatile organic compounds (VOCs). Herein, a lab-scale continuous reactor is used to investigate the photocatalytic performance toward ethylbenzene (EB) vapor removal over TiO₂ nanoparticles immobilized on glass fiber tissue. The role of the reactive species in the removal of EB and the degradation pathway were studied. Firstly, the effect of key operating parameters such as EB concentration (13, 26, 60 mg/m³), relative humidity levels (From 5 to 80%), gas carrier composition (dry air + EB, O₂ + EB and N₂ + EB) and ultraviolet (UV) radiation wavelength (UV-A _365 nm, UV-C _254 nm) were explored. Then, using superoxide dismutase and tert-butanol as trapping agents, the real contribution of superoxide radical anion (O₂^.-) and hydroxyl radicals (OH^.) to EB removal was quantified. The results show that (i) small water vapor content enhances the EB degradation; (ii) the reaction atmosphere plays an important role in the photocatalytic process; and (iii) oxygen atmosphere/UV-C radiation shows the highest EB degradation percentage. The use of radical scavengers confirms the major contribution of the hydroxyl radical to the photocatalytic mechanism with 75% versus 25% for superoxide radical anion.

Synthesis of BiOI@NH2-MIL125(Ti)/Zeolite as a novel MOF and advanced hybrid oxidation process application in benzene removal from polluted air stream

One of the popular process in volatile organic compounds removal in gas phase is advanced oxidation process. We in this research, synthesized BiOI@NH2-MIL125(Ti)/Zeolite nanocomposite as a novel nanocomposite to degradation of benzene in hybrid advanced oxidation process. The nanocomposite synthesized via solvothermal method. The effect of airflow, ozone gas concentration, hydrogen peroxide concentration, relative humidity and initial benzene concentration are the main parameters in the UV/O3/H2O2/ nanocomposite hybrid process that were studied. The characterization by XRD, FT-IR, FESEM, EDS element mapping, TEM, BET, and UV-vis spectra indicated that nanocomposite were well synthesized. Optimal operating conditions of the process were determined at air flow of 0.1 l/min, ozone concentration of 0.3 mg/min, hydrogen peroxide concentration of 150 ppm, relative humidity of 45 ± 3% and benzene concentration of 50 ppmv. Under these conditions, more than 99% of benzene was degraded. The synergistic effect coefficient of the mechanisms is 1.53. The nanocomposite had good stability in the hybrid process and remained above 99% efficiency up to 5 times. The ozone concentration residual the system was reported to be negligible (0.013 mg/min). The CO and CO2 emissions in the hybrid process was higher than other processes, which indicates better mineralization in the hybrid process. Formaldehyde, octane, noonan, phenol, decanoic acid were reported as the main by-products. The results indicated that UV/O3/H2O2/ nanocomposite hybrid process has fantastic efficiency in the degradation of benzene as one of the indicators of VOCs.

Degradation of gaseous volatile organic compounds (VOCs) by a novel UV-ozone technology

In this study, a UV-assisted ozonation (UV/O₃) process for the degradation of VOCs emissions with a final scrubbing phase was implemented to evaluate the removal efficiency of toluene and to prevent the release of polluting intermediates of the single-step process. Inlet toluene concentration and applied voltage were varied in order to investigate several operating conditions. The results highlighted that at higher inlet concentration the abatement of toluene was lower, while increase in ozone concentration led to an increase of the degradation efficiencies. The additional water scrubbing step enhanced the abatement of UV/O₃ up to 98.5%, due to the solubilisation of ozone and by-products in the process water and, thus, the further oxidation of the contaminants within this phase. A maximum Elimination Capacity (EC_max) of 22.6 g m⁻³ h⁻¹ was achieved with the UV/O₃ + Scrubbing. The combined system boosted higher performance and stability compared to the stand-alone (UV/O₃) process along with a more economical and environmental sustainability.

Nano Metal-Containing Photocatalysts for the Removal of Volatile Organic Compounds: Doping, Performance, and Mechanisms

Volatile organic compounds (VOCs) in indoor air are considered a major threat to human health and environmental safety. The development of applicable technologies for the removal of VOCs is urgently needed. Nowadays, photocatalytic oxidation (PCO) based on metal-containing photocatalysts has been regarded as a promising method. However, unmodified photocatalysts are generally limited in applications because of the narrow light response range and high recombination rate of photo-generated carriers. As a result, nano metal-containing photocatalysts doped with elements or other materials have attracted much attention from researchers and has developed over the past few decades. In addition, different doping types cause different levels of catalyst performance, and the mechanism for performance improving is also different. However, there are few reviews focusing on this aspect, which is really important for catalyst design and application. This work aims to give a comprehensive overview of nano metal-containing photocatalysts with different doping types for the removal of VOCs in an indoor environment. First, the undoped photocatalysts and the basic mechanism of PCO is introduced. Then, the application of metal doping, non-metal doping, co-doping, and other material doping in synthetic metal-containing photocatalysts are discussed and compared, respectively, and the synthesis methods, removal efficiency, and mechanisms are further investigated. Finally, a development trend for using nano metal-containing photocatalysts for the removal of VOCs in the future is proposed. This work provides a meaningful reference for selecting effective strategies to develop novel photocatalysts for the removal of VOCs in the future.