Development of spray pyrolysis-synthesised Bi2O3 thin films for photocatalytic applications.

Photocatalysis is a green and cost-effective approach to environmental remediation. While TiO2 is considered one of the benchmark photocatalysts, alternative materials such as Bi2O3 have recently attracted increasing scientific attention as prospective visible light photocatalysts. This study aimed to develop a strategy for Bi2O3 thin film deposition via ultrasonic spray pyrolysis and systematically study process variables for the deposition of ß-Bi2O3 thin films for photocatalytic applications. To achieve the aim, the precursor solution concentration as well as deposition and annealing temperature were optimised. The structural, optical, morphological, chemical and wettability properties of the obtained Bi2O3 thin films were investigated with respect to the effect on the photocatalytic oxidation of 10 ppm methyl orange (MO). The highest photocatalytic activity (48% in 5 h) under UV-A was recorded for the ß-Bi2O3 film deposited using 0.1 M precursor solution at 300 °C and heat-treated for 1 h in air at 350 °C. Deposition at 300 °C resulted in an amorphous film structure, whereas annealing at 350 °C led to the formation of the ß-Bi2O3 phase with the dominant facet orientation (220). These results show the suitability of spray pyrolysis for the deposition of Bi2O3 thin films with promising results for MO dye degradation, expanding the range of suitable photocatalytic materials.

Transparent TiO2 thin films with high photocatalytic activity for indoor air purification.

The development of low-material-quantity, transparent, anatase TiO2 nanoparticle free thin films as photocatalytic materials together with a profound understanding of their photocatalytic activity under ultraviolet (UV-A) and visible (VIS) light is crucial for environmentally friendly indoor air photocatalytic coatings. In this work, a TiO2 thin film modified by an increased amount of acetylacetone in the precursor solution with a material quantity of 0.2 mg cm-2 was successfully deposited on a borosilicate glass substrate by ultrasonic spray pyrolysis. VOC degradation as a single model pollutant and in mixtures under different operating conditions was studied in a multi-section continuous flow reactor. Under UV-A the reaction rate constants for heptane and toluene oxidation as individual pollutants were 1.7 and 0.9 ppm s-1, respectively. In 9 ppm VOC mixtures of acetaldehyde, acetone, heptane and toluene all the compounds were completely oxidized in a reaction time of less than 50 s. The TiO2 film showed moderately high photocatalytic activity under VIS light. The conversions of acetaldehyde, acetone, heptane and toluene in 9 ppm VOC mixtures under VIS light reached 100, 100, 78 and 31%, respectively. The synthesized TiO2 film shows promising ability in indoor air purification from VOCs. The results of this study give an extensive estimation of the thin film's photocatalytic efficiency and provide valuable data for future applications in environmental remediation.

Optimization of the Sb2S3 Shell Thickness in ZnO Nanowire-Based Extremely Thin Absorber Solar Cells.

Extremely thin absorber (ETA) solar cells made of ZnO/TiO2/Sb2S3 core-shell nanowire heterostructures, using P3HT as the hole-transporting material (HTM), are of high interest to surpass solar cell efficiencies of their planar counterpart at lower material cost. However, no dimensional optimization has been addressed in detail, as it raises material and technological critical issues. In this study, the thickness of the Sb2S3 shell grown by chemical spray pyrolysis is tuned from a couple of nanometers to several tens of nanometers, while switching from a partially to a fully crystallized shell. The Sb2S3 shell is highly pure, and the unwanted Sb2O3 phase was not formed. The low end of the thickness is limited by challenges in the crystallization of the Sb2S3 shell, as it is amorphous at nanoscale dimensions, resulting in the low optical absorption of visible photons. In contrast, the high end of the thickness is limited by the increased density of defects in the bulk of the Sb2S3 shell, degrading charge carrier dynamics, and by the incomplete immersion of the P3HT in the structure, resulting in the poor hole collection. The best ETA solar cell with a short-circuit current density of 12.1 mA/cm2, an open-circuit voltage of 502 mV, and a photovoltaic conversion efficiency of 2.83% is obtained for an intermediate thickness of the Sb2S3 shell. These findings highlight that the incorporation of both the absorber shell and HTM in the core-shell heterostructures relies on the spacing between individual nanowires. They further elaborate the intricate nature of the dimensional optimization of an ETA cell, as it requires a fine-balanced holistic approach to correlate all the dimensions of all the components in the heterostructures.

Copper-zinc oxide heterojunction catalysts exhibiting enhanced photocatalytic activity prepared by a hybrid deposition method.

Heterojunction copper-zinc oxide catalysts were prepared by a hybrid two-step methodology comprising hydrothermal growth of ZnO nanorods (ZnO-NR) followed by deposition of Cu2O nanoparticles using an advanced gas deposition technique (AGD). The obtained bicatalysts were characterized by SEM, AFM, XRD, XPS, PL and spectrophotometry and revealed well-dispersed and crystalline Cu2O nanoparticles attached to the ZnO-NR. The adsorption properties and photocatalytic degradation of Orange II dye in water solutions were measured. It was found that the bicatalysts exhibited a conversion rate and quantum yield that both were about 50% higher compared with ZnO-NR alone, which were attributed to the intrinsic electric field created at the p-n junction formed at the Cu2O/ZnO interface facilitating charge separation of electron-hole pairs formed upon interband photon absorption. The interpretation was evidenced by efficient quenching of characteristic deep level ZnO photoluminescence bands and photoelectron core-level energy shifts. By comparisons with known energy levels in Cu2O and ZnO, the effect was found to be most pronounced for the non-polar ZnO-NR side facets, which accounted for about 95% of the exposed surface area of the catalyst and hence the majority of dye adsorption. It was also found that the dye adsorption capacity of the ZnO nanorods increased considerably after Cu2O deposition thereby facilitating the oxidation of the dye. The results imply the possibility of judiciously aligning band edges on structurally controlled and well-connected low-dimensional semiconductor nanostructures using combined two-step synthesis techniques, where in particular vacuum-based techniques such as AGD allow for growth of well-connected nanocrystals with well developed heterojunction interfaces.

Correction: Copper-zinc oxide heterojunction catalysts exhibiting enhanced photocatalytic activity prepared by a hybrid deposition method.

[This corrects the article DOI: 10.1039/D1RA00691F.].

TiO2 thin films by ultrasonic spray pyrolysis as photocatalytic material for air purification.

In this study, we showed that the TiO2 thin films deposited onto window glass are practicable for air purification and self-cleaning applications. TiO2 films were deposited onto window glass by ultrasonic spray pyrolysis method. Different deposition temperatures were used in the range of 250-450°C. The structural, morphological, optical properties and surface chemical composition were investigated to understand probable factors affecting photocatalytic performance and wettability of the TiO2 thin films. The TiO2 thin films were smooth, compacted and adhered adequately on the substrate with a thickness in the range of 100-240 nm. X-ray diffraction patterns revealed that all the TiO2 thin films consisted of anatase phase structure with the mean crystallite size in the range of 13-35 nm. The optical measurements showed that the deposited films were highly transparent (approx. 85%). The wettability test results showed that the TiO2 thin films sprayed at 350°C and 450°C and annealed at 500°C for 1 h were superhydrophilic. The photocatalytic activity of the films was tested for the degradation of methyl tert-butyl ether (MTBE) in multi-section plug-flow reactor. The TiO2 film deposited at 350°C exhibited the highest amount of conversion of MTBE, approximately 80%.

Modification of light absorption in thin CuInS2 films by sprayed Au nanoparticles.

The chemical spray pyrolysis method was used to deposit CuInS2 (CIS) thin films and Au nanoparticles (NPs) in two configurations: glass/Au-NP layer covered with CuInS2 film (Au-NP/CIS) and glass/CuInS2 films covered with Au-NP layer (CIS/Au-NP). According to X-ray diffraction (XRD), the spray of 2 mM HAuCl4 aqueous solution with a volume of 2.5 to 15 ml onto a glass substrate at 340°C results in metallic Au nanoparticles with a similar mean crystallite size in the range of 30 - 38 nm. The mean crystallite sizes remain in the range of 15 - 20 nm when grown onto a CIS film. The prepared films show plasmonic light absorption with increasing intensity in the spectral range of 500- 800 nm when increasing the volume of HAuCl4 solution sprayed. When compared to bare CIS on glass, the absorptance was increased ca. 4.5 times in the case of glass/Au-NP/CIS and ca. 3 times in the case of glass/CIS/Au-NP configuration. The glass/Au-NP/CIS configuration had an advantage since Au-NP could be embedded without chemically damaging the CIS.