Recent advancement in conjugated polymers based photocatalytic technology for air pollutants abatement: Cases of CO2, NOx, and VOCs.

According to World Health Organization (WHO) survey, air pollution has become the major reason of several fatal diseases, which had led to the death of 7 million peoples around the globe. The 9 people out of 10 breathe air, which exceeds WHO recommendations. Several strategies are in practice to reduce the emission of pollutants into the air, and also strict industrial, scientific, and health recommendations to use sustainable green technologies to reduce the emission of contaminants into the air. Photocatalysis technology recently has been raised as a green technology to be in practice towards the removal of air pollutants. The scientific community has passed a long pathway to develop such technology from the material, and reactor points of view. Many classes of photoactive materials have been suggested to achieve such a target. In this context, the contribution of conjugated polymers (CPs), and their modification with some common inorganic semiconductors as novel photocatalysts, has never been addressed in literature till now for said application, and is critically evaluated in this review. As we know that CPs have unique characteristics compared to inorganic semiconductors, because of their conductivity, excellent light response, good sorption ability, better redox charge generation, and separation along with a delocalized π-electrons system. The advances in photocatalytic removal/reduction of three primary air-polluting compounds such as CO2, NOX, and VOCs using CPs based photocatalysts are discussed in detail. Furthermore, the synergetic effects, obtained in CPs after combining with inorganic semiconductors are also comprehensively summarized in this review. However, such a combined system, on to better charges generation and separation, may make the Adsorb & Shuttle process into action, wherein, CPs may play the sorbing area. And, we hope that, the critical discussion on the further enhancement of photoactivity and future recommendations will open the doors for up-to-date technology transfer in modern research.

Low-Temperature Detection of Sulfur-Hexafluoride Decomposition Products Using Octahedral Co3O4-Modified NiSnO3 Nanofibers.

Sulfur hexafluoride (SF6) is widely used in electrical equipment because of its excellent insulating properties. The type of internal fault in the power system can be identified by detecting SF6 decomposition products. In this manuscript, we report a novel sensing material based on octahedral Co3O4-modified NiSnO3 nanofibers synthesized via a two-step process based on electrospinning followed by a hydrothermal method for detecting the SF6 decomposition products. From the evaluation of various characterization techniques, it was determined that the Co3O4 octahedra adhered inflexibly to the surface of the NiSnO3 nanofibers, which consist of smaller particles and provide a huge surface area for the adsorption of an enormous amount of gas species. Planar-type chemical gas sensors were devised, and their gas detecting performance against SF6 decomposition products was systematically investigated. A comparison of the sensitivity properties of different amounts of charged Co3O4 octahedra in NiSnO3 nanofibers shows that the S-2-based Co3O4@NiSnO3 composite has a high selectivity for 100 ppm SO2F2 gas with a high sensing response of 22.5 at a relatively low temperature of 50 °C with a moderate response/recovery interval (∼200/∼268 s) and a low detection limit (5 ppm) over other interfering gases, such as SOF2, SO2, and H2S. Interestingly, the sensing properties of the fabricated sensors based on the Co3O4@NiSnO3 composites for the SO2F2 gas were improved in terms of lower operating temperatures, higher gas responses, and mild response/recovery intervals, which could be attributed to the unique microstructure effect, the catalytic influence of Co3O4 octahedra, and the creation of p/n junctions to increase the charge transfer and diffusion rate within the catalytic assembly of the sensor materials. This work highlights the importance of the heterostructure design in the construction of high-performance gas sensors for the real-time detection of SF6 decomposition products.

Design of highly sensitive and selective ethanol sensor based on α-Fe2O3/Nb2O5 heterostructure.

The introduction of heterostructures is a new approach in gas sensing due to their easy and quick transport of charges. Herein, facile hydrothermal and solid-state techniques are employed to synthesize an α-Fe2O3/Nb2O5 heterostructure. The morphology, microstructure, crystallinity and surface composition of the synthesized heterostructures are investigated by scanning electron microscope, transmission electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy and Brunauer-Emmett-Teller analyses. The successful fabrication of the heterostructures was achieved via the mutual incorporation of α-Fe2O3 nanorods with Nb2O5 interconnected nanoparticles (INPs). A sensor based on the α-Fe2O3(0.09)/Nb2O5 heterostructure with a high surface area exhibited enhanced gas-sensing features, maintaining high selectivity and sensitivity, and a considerable recovery percentage towards ethanol gas. The sensing response of the α-Fe2O3(0.09)/Nb2O5 heterostructure at lower operating temperature (160 °C) is around nine times higher than a pure Nb2O5 (INP) sensor at 180 °C with the flow of 100 ppm ethanol gas. The sensors also show excellent selectivity, good long-term stability and a rapid response/recovery time (8s/2s, respectively) to ethanol. The superior electronic conductivity and upgraded sensitivity performance of gas sensors based on the α-Fe2O3(0.09)/Nb2O5 heterostructure are attributed due to its unique structural features, high specific surface area and the synergic effect of the n-n heterojunction. The promising results demonstrate the potential application of the α-Fe2O3(0.09)/Nb2O5 heterostructure as a good sensing material for the fabrication of ethanol sensors.

Development of high-performance sensor based on NiO/SnO2 heterostructures to study sensing properties towards various reducing gases.

In this work, we report the spontaneous formation of NiO nanoparticles-decorated onto smooth SnO2 nanofibers, which is an inexpensive and scalable method for yielding a high composite surface area via a simple two-step synthesis process based on electrospinning and the hydrothermal method. A Nickel Oxide proton-conducting electrolyte is deposited homogeneously over a large surface area in a transparent solution, mixed and decorated onto Tin dioxide nanofibers, as evidenced by cross sectional imaging of the electrospun nanofibers. The composite based on nanoparticle-decorated fibers enlarges the surface area of the exposed electrolyte, which fundamentally improves the overall gas sensing performance. The crystal structure, morphology, and physio-chemical surface state of the NiO/SnO2-based specimen are comprehensively examined using XRD, SEM, TEM, HRTEM, EDX, and photoelectron (XPS) spectroscopy. The composite based on NiO/SnO2 nanoparticle-decorated fibers exhibits an optimistic mesoporous nature with a huge specific area, which is key for superior gas sensors. The result reveals that NiO/SnO2 nanoparticle-decorated fibers with an average size of 180-260 nm in diameter, where the average length of fibers was about 1.5 µm. The composite-based heterojunction of NiO/SnO2 nanoparticle-decorated fibers enhances the adsorption of oxygen molecules, which show fast response, good selectivity and quick recovery speed against ethanol gas at an optimal temperature of about 160 °C. The maximum sensitivity response of the sensor-based composite NiO/SnO2 nanoparticle-decorated fibers was 23.87 in respect of 100 ppm ethanol gas at a low temperature of 160 °C; this is approximately about 7.2 times superior to that of pure SnO2 nanofibers. The superior gas sensing capabilities of a composite based on NiO/SnO2 nanoparticle-decorated fibers may be attributable to the enhanced catalytic effect of the small sized NiO nanoparticles on smooth SnO2 nanofibers, together with the p/n heterojunction effects between NiO and SnO2 heterostructures.

A novel ethanol gas sensor based on α-Bi2Mo3O12/Co3O4 nanotube-decorated particles.

A novel composite based on α-Bi2Mo3O12/Co3O4 nanotube-decorated particles was successfully synthesized using a highly efficient and facile two step system using electrospinning and hydrothermal techniques. The small size Co3O4 nanoparticles were uniformly and hydrothermally developed on the electrospun α-Bi2Mo3O12 nanotubes. The pure α-Bi2Mo3O12 nanofibers and composite based on α-Bi2Mo3O12/Co3O4 were examined using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analyses. From the BET measurements, the composite based on α-Bi2Mo3O12/Co3O4 exhibits a large specific surface area of 54 m2 g-1 with mesopore diameter ranges of 2-10 nm, which is mainly attributed to the remarkable and dominant enhancement in gas sensing as compared to that of the pure α-Bi2Mo3O12 nanofibers (38 m2 g-1) and Co3O4 nanoparticles (32 m2 g-1), respectively. In this work, the novel composite based on α-Bi2Mo3O12/Co3O4 presented a high sensitivity of 30.25 with a quick response/recovery speed towards 100 ppm ethanol at an optimal working temperature of 170 °C, as compared to the pure α-Bi2Mo3O12 nanofibers and Co3O4 nanoparticles, which display a sensitivity of 13.10 and 2.99 at an optimal working temperature of 220 °C and 280 °C. The sensing performance of the composite based on the α-Bi2Mo3O12/Co3O4 sensor exhibits a superior sensing performance towards ethanol, which might be owed to the enormous number of superficial oxygen species, the small size catalytic effect of the Co3O4 nanoparticles and the interfacial effect formed between the n-type α-Bi2Mo3O12 and p-type Co3O4 leading to a high charge carrier concentration. This is a novel investigation of a composite based on an α-Bi2Mo3O12/Co3O4 sensor in the gas sensing era, which might be of vital importance in applications in the advanced gas sensing field.

Marangoni effect induced macro porous surface films prepared through a facile sol-gel route.

Based on TiO2 as a model system, the sol-gel one step facile method is established to fabricate the macro-porous morphology films on the basis of Marangoni effect. In this proposed mechanism, the binary mixture of hydrophilic CuCl2 and lipophilic Ti-O network is used in sol to produce phase separation. A suitable evaporation rate in the gel film process leads to the macro-porous film due to Marangoni effect. It is observed that the macro-porous morphology of the film sustains during the annealing process, which suggests the creation of porous surface morphology in gel film stage rather than due to annealing. To analyze the preparation mechanism, the sol-gel process and microstructure of films are examined using TG-DTA, SEM, TEM, XRD, Raman, UV-Vis, XPS and FTIR. Furthermore, the optical-thermal properties are studied for the potential applications of such porous surface films as solar selective absorber.