Chitosan microspheres as a template for TiO₂and ZnO microparticles: studies on mechanism, functionalization and applications in photocatalysis and H₂S removal

Abstract

In the past few decades, several studies have used nanoparticles for photocatalytic reactions. For practical applications, the use of nanomaterials may not be advantageous due to the difficulties in removing them from processed liquids, and they also pose possible health risks. We have developed a procedure that uses chitosan to convert nanosized photocatalysts into micron sized materials without losing their efficiency or surface area. Additionally, the synthetic method offers the possibility of adding functionality like macroporosity and doping carbon or gold nanoparticles. The synthesis involves ultrasonic emulsification of tetradecane in an aqueous chitosan solution containing photocatalytic nanoparticles.Tetradecane-core chitosan/photocatalyst composite-shelled microspheres were produced during the ultrasonic emulsification process. Calcination of these microspheres resulted in the formation of carbon doped micron-sized photocatalytic particles with macroporous structure. Detailed characterisations were carried out using dynamic light scattering, zeta potential, SEM, TEM, BET, XRD and XPS measurements. A possible mechanism for the formation of micron-sized photocatalytic particles is proposed. The photocatalytic efficiencies of synthesised microparticles and their reusability through filtration were evaluated and compared with that of starting nanomaterials using two organic dyes as model pollutants. One of the catalysts (gold doped photocatalyst) was also tested for H 2 S gas removal by adsorption. The regeneration of the adsorbent was also achieved after room temperature photocatalysis.The results indicate that the synthetic procedure can be used to produce macroscale photocatalysts with a size range of 10-20 mm as efficient as the starting nanopowders (size range of 20-50 nm).

Comparison of the photocatalytic efficiencies of continuous stirred tank reactor (CSTR) and batch systems using a dispersed micron sized photocatalyst

“…The aim of this work was to compare the efficiency of batch and continuous ow reactors using a carbon-doped TiO 2 micronsized catalyst (10 mm) synthesised in our previous work using chitosan microspheres as a template, 19 named TiO 2 -Micro, was chosen as the photocatalyst. 20 A detailed experimental procedure was discussed in our previous report. 20 A schematic diagram is shown in Scheme 1.…”

“…20 A detailed experimental procedure was discussed in our previous report. 20 A schematic diagram is shown in Scheme 1.…”

“…As reported from previous studies, RB undergoes a faster degradation rate compared to that of MY. 20 For example, considering 90% degradation, the amounts decomposed were 20-37 mmol per day for MY and 40-65 mmol per day for RB. The result in Fig.…”

Treatment of Aquaculture Wastewater through Chitin/ZnO Composite Photocatalyst

“…When ZnO and other semiconductor particles are in close contact with the aqueous solution, the hydroxyl groups will form and adhere to the semiconductor surface. At the same time, owing to the valence band site of the semiconductor, ZnO is lower than the oxidation potential of the hydroxyl group [27]; the positively charged holes on the semiconductor surface will be first trapped by the surface hydroxyl radicals, producing hydroxyl radicals with strong oxidation via light irradiation: ZnO + hv → e − +ZnO(h+)…”

Enhancement Photocatalytic Activity of the Heterojunction of Two-Dimensional Hybrid Semiconductors ZnO/V2O5

“…In these systems, the main absorber is the secondary semiconductor while the role of ZnO is principally limited to the charge curriers transport. That notwithstanding, some interesting approaches to directly improve ZnO visible-light absorption have been also attempted; namely by creating electronic levels within the ZnO band gap, by metal or non-metal doping, or surface modification via organic materials grafting [22][23][24][25]. Most attempts to improve the photocatalysis of organic contaminants by optimizing the adsorption of the substrates upon the photocatalyst mainly concern the increment of its specific surface area, so the utilization of 2D layered materials that have larger specific surface areas-a great number of active sites on the surface and superior electron mobility that facilitates the transfer and separation of photogenerated electrons and holes-is a good strategy for constructing effective photocatalyst [26,27].…”