Tze Hao Tan

Effects of organic hole scavengers on the photocatalytic reduction of selenium anions

Abstract The photocatalytic reduction of selenium anions, selenate (Se(VI)) and selenite (Se(IV)) to elemental selenium (Se) over UV-illuminated TiO2 was performed using formic acid, acetic acid, methanol, ethanol, sucrose and salicylic acid as the organic hole scavengers. Photoreduction was only observed in the presence of formic acid, methanol or ethanol. The fastest rate of Se ions photoreduction was observed in the presence of formic acid followed by methanol and ethanol. This was attributed to the ability of formate ions to adsorb onto TiO2 in the presence of Se ions, its fast mineralisation rate and its ability to form reducing radicals quickly. For the methanol and ethanol systems, these two organic compounds could not compete with Se ions for the TiO2 surface and were not easily mineralised. The photocatalytic reduction of Se ions observed in the presence of these two organic compounds was attributed to their ability to form reducing radicals. When formic acid was used, optimum pH values at pH 3.5 and 4.0 was encountered for the Se(VI) and Se(IV) photoreduction, respectively. When methanol and ethanol were used as the hole scavenger in the pH range of 2.2–4.0, the greatest extent of Se ions photoreduction was encountered at pH 2.2. This suggests the different role of formic acid and methanol/ethanol in the photoreduction of Se ions.

Highly Selective and Stable Reduction of CO2 to CO by a Graphitic Carbon Nitride/Carbon Nanotube Composite Electrocatalyst.

A stable and selective electrocatalyst for CO2 reduction was fabricated by covalently attaching graphitic carbon nitride onto multiwall carbon nanotubes (g-C3 N4 /MWCNTs). The as-prepared composite is able to reduce CO2 exclusively to CO with a maximum Faraday efficiency of 60 %, and no decay in the catalytic activity was observed even after 50 h of reaction. The enhanced catalytic activity towards CO2 reduction is attributed to the formation of active carbon-nitrogen bonds, high specific surface area, and improved material conductivity of the g-C3 N4 /MWCNT composite.

A sea-change: manganese doped nickel/nickel oxide electrocatalysts for hydrogen generation from seawater

The practical implementation of electrolytic water splitting systems (especially those powered by renewable energy resources, such as solar and wind) requires active and stable catalysts for the hydrogen evolution reaction (HER). The development of catalysts that can compete with, or exceed, the performance of the exorbitant platinum (Pt)-based benchmark is highly desirable. Here, we demonstrate the development of a highly active HER catalyst electrode, exhibiting Pt-like performances in both neutral electrolytes and natural seawater. The catalyst was obtained by pyrolysing a manganese-based metal organic framework (Mn-MOF) on nickel foam (Ni-F). We discovered for the first time that nickel foam not only acts as the substrate for catalyst growth but also provides nickel species that interact with the Mn-MOF, resulting in the formation of Mn doped nickel oxide/nickel hetero-structures on Ni-F (Mn–NiO–Ni/Ni-F). The potential utilization of this catalyst electrode for commercial applications was demonstrated in a self-customized water electrolyzer pack powered by photovoltaic cells.