Synthesis of reduced graphene oxide functionalized with methyl red dye and its role in enhancing photoactivity in TiO2–IL/WO3 composite for toluene degradation

Multistep Removal System of Gaseous Toluene: Adsorption, Electrochemical, and Photolytic Treatments

A large amount of atmospheric emissions result from various anthropogenic activities worldwide. Given the complexity of volatile organic compounds (VOCs) and their different adsorption capacities, redox potentials, and photolytic properties, an air purification system for the removal of VOCs that combines multiple physical processes was proposed in this study using toluene as an example. These processes include, in the first step, an adsorption treatment (AT) with activated carbon (AC), where toluene adsorption results from the insertion of aromatic rings (nonpolar groups) between the graphitic carbon planes, as demonstrated by the Raman spectroscopy; in the second step, electrochemical treatment (ECT) using TiO2,nt|Ti||SS-304 electrodes applying an electric field to accelerate the oxidation of toluene through the production of free radicals (⋅OH), hydroperoxyl radicals and benzyl groups, followed by the rupture of aromatic rings to generate aliphatic compounds and the consequent mineralization to CO, CO2, and H2O; in the third step, photolytic treatment (PT) with a 254-nm UV lamp for toluene degradation is used, which is influenced by the addition of radicals, such as ⋅OH or ⋅O- 2ad, to transform toluene into either benzene or phenol. The multistep system integrating AT, ECT and PT was more efficient overall (99.58 %) than the individual treatments (AT=50.29 %, ECT=44.38 %, and PT=52.71 %) as evaluated by gas chromatography with a BID detector; it showed enhanced efficiency enabled by the synergistic effects of combining multiple technologies to enhance the overall toluene degradation efficiency and flexibility. The multistage systems can be adapted to specific contamination conditions and process requirements with the generation of residual toluene, phenol, and aliphatic compounds and possible mineralization to molecules such as CO2, CO, and H2O. This small and portable multistep system provides a novel approach for treating outdoor and/or indoor air contaminated with toluene.

Efficient Photocatalytic Degradation of Gaseous Benzene and Toluene over Novel Hybrid PIL@TiO2/m-GO Composites

In this work, the PIL (poly ionic liquid)@TiO2 composite was designed with two polymerized ionic liquid concentrations (low and high) and evaluated for pollutant degradation activity for benzene and toluene. The results showed that PIL (low)@TiO2 composite was more active than PIL (high)@TiO2 composites. The photodegradation rate of benzene and toluene pollutants by PIL (low)@TiO2 and PIL (high)@TiO2 composites was obtained as 86% and 74%, and 59% and 46%, respectively, under optimized conditions. The bandgap of TiO2 was markedly lowered (3.2 eV to 2.2 eV) due to the formation of PIL (low)@TiO2 composite. Besides, graphene oxide (GO) was used to grow the nano-photocatalysts’ specific surface area. The as-synthesized PIL (low)@TiO2@GO composite showed higher efficiency for benzene and toluene degradation which corresponds to 91% and 83%, respectively. The resultant novel hybrid photocatalyst (PIL@TiO2/m-GO) was prepared and appropriately characterized for their microstructural, morphology, and catalytic properties. Among the studied photocatalysts, the PIL (low)@TiO2@m-GO composite exhibits the highest activity in the degradation of benzene (97%) and toluene (97%). The ultimate bandgap of the composite reached 2.1 eV. Our results showed that the as-prepared composites hold an essential role for future considerations over organic pollutants.