Photoluminescence of dense nanocrystalline titanium dioxide thin films: effect of doping and thickness and relation to gas sensing

The photoluminescence (PL) of dense nanocrystalline (anatase) TiO(2) thin films is reported as a function of calcination temperature, thickness, and tungsten and nickel doping. The dependence of the optical absorption, Raman spectra, and PL spectra on heat treatment and dopants reveals the role of oxygen vacancies, crystallinity, and phase transformation in the performance of TiO(2) films used as gas sensors. The broad visible PL from defect states of compact and undoped TiO(2) films is found to be much brighter and less sensitive to the presence of oxygen than that of mesoporous films. The dense nanocrystalline grains and the nanoparticles comprising the mesoporous film are comparable in size, demonstrating the importance of film morphology and carrier transport in determining the intensity of defect photoluminescence. At higher calcination temperatures, the transformation to rutile results in the appearance of a dominant near-infrared peak. This characteristic change in the shape of the PL spectra demonstrates efficient capture of conduction band electrons by the emerging rutile phase. The W-doped samples show diminished PL with quenching on the red side of the emission spectrum occurring at lower concentration and eventual disappearance of the PL at higher W concentration. The results are discussed within the context of the performance of the TiO(2) thin films as CO gas sensors and the chemical nature of luminescent defects.     

Removal of endosulfan in a sequencing batch reactor: addition of granular activated carbon as improvement strategy

A granular activated carbon‐sequencing batch reactor (GAC‐SBR) was used to assess the removal of organochlorine endosulfan pesticide. The reactor operated in three stages: (I) starter and stabilization; (II) addition of 4 mg/L of endosulfan in feed; and (III) a single addition of 1 g/L of GAC to mixed liquor. During the 249 days of operation, the removal efficiency of COD was 96 ± 2%; for ‐N 72 ± 1%; and for PO₄^?3‐P 48 ± 13%. Was eliminated the 79% of endosulfan in stage II and 99% in stage III, not found its metabolite (endosulfan sulphate) in the reactor effluent. A consortium of eight bacterial strains was identified in the reactor stages, assessing five of them in the presence of 4 mg endosulfan/L by growth kinetics. According to the results, the joint action of the consortium and GAC addition is the responsible of eliminating the pesticide.     

Do zoom meetings really help? A comparative analysis of synchronous and asynchronous online learning during Covid-19 pandemic

Background

Online learning and teaching were globally popularized due to the impact of Covid-19. The pandemic has made both synchronous and asynchronous online learning inevitable in regions privileged with the technological affordance.

Aims

This study was designed to examine and compare the effectiveness of both learning modes through the Community of Inquiry framework.

Materials & Methods

Comparative analyses on a sample of N = 170 undergraduate students who took both synchronous and asynchronous online courses in Spring 2021.

Results

The paired-sample T-tests results indicated a significant difference in social presence, cognitive presence and self-evaluated performance.

Discussion & Conclusion

Teaching presence significantly influenced social presence and cognitive presence in both learning modes. However, under synchronous learning mode, social presence significantly impacted self-evaluation, grades and school identification. While social presence only influenced school identification under asynchronous learning mode. Theoretical and practical implications were also included.