ABSTRACT
In pursuit of efficient solar energy to chemical energy conversion through band engineering of wide-bandgap photocatalysts such as TiO2, a compromise occurs between a narrow bandgap and high-redox-capacity photo-induced charge carriers, which impairs the potential advantages associated with the widened absorption range. The key to this compromise is an integrative modifier that can simultaneously modulate both the bandgap and band edge positions. Herein, we theoretically and experimentally demonstrate that oxygen vacancies occupied by boron-stabilized hydrogen pairs (OVBH) serve as an integrative band modifier. Compared to hydrogen-occupied oxygen vacancies (OVH), which require the aggregation of nanosized anatase TiO2 particles, oxygen vacancies coupled with boron (OVBH) can be easily introduced into large and highly crystalline TiO2 particles, as shown by density functional theory (DFT) calculations. The coupling with interstitial boron facilitates the introduction of paired hydrogen atoms. The red-colored {001} faceted anatase TiO2 microspheres with OVBH benefit from the narrowed bandgap of 1.84 eV and the down-shifted band position. These microspheres not only absorb long-wavelength visible light up to 674 nm but also enhance visible-light-driven photocatalytic oxygen evolution.
ABSTRACT
The strong band-to-band absorption of photocatalysts spanning the whole visible-light region (400-700â nm) is critically important for solar-driven photocatalysis. Although it has been actively and widely used as a photocatalyst for various reactions in the past four decades, TiO2 has a very poor ability to capture the whole spectrum of visible light. In this work, by controlling the spatially homogeneous distribution of boron and nitrogen heteroatoms in anatase TiO2 microspheres with a predominance of high-energy {001} facets, a strong visible-light absorption spectrum with a sharp edge beyond 680â nm has been achieved. The red TiO2 obtained with homogeneous doping of boron and nitrogen shows no increase in defects like Ti3+ that are commonly observed in doped TiO2 . More importantly, it has the ability to induce photocatalytic water oxidation to produce oxygen under the irradiation of visible light beyond 550â nm and also the photocatalytic reduction of water to produce hydrogen under visible light. These results demonstrate the great promise of using red TiO2 for visible-light photocatalytic water splitting and also reveal an attractive strategy for realizing the wide-spectrum visible-light absorption of wide-band-gap oxide photocatalysts.
ABSTRACT
In this paper, a new core-shell nanostructured magnetic bio-based composite was prepared by immobilizing persimmon tannin (PT) onto Fe3O4@SiO2 microspheres, and the as designed Fe3O4@SiO2@PT was utilized for adsorptive recovery of Au(III) and Pd(II). The preparation, morphology, composition and magnetic property of Fe3O4@SiO2@PT were characterized. Adsorption parameters of Fe3O4@SiO2@PT towards Au(III) and Pd(II) including initial pH, reaction time, initial concentration of metal ions, effect of acidity and interference of coexisting metal ions were investigated. It is sufficiently confirmed that silica was coated on Fe3O4 and persimmon tannin was immobilized on aminated Fe3O4@SiO2. The thickness of silica and loaded persimmon tannin are around 18â¯nm and 14â¯nm, respectively. With only 1.00â¯wt% of persimmon tannin, however, the maximum adsorption capacities of Fe3O4@SiO2@PT for Au(III) and Pd(II) were as high as 917.43 and 196.46â¯mg·g-1, respectively. In addition, after adsorption of Au(III) and Pd(II), the magnetization saturation values (Ms) of Fe3O4@SiO2@PT were high enough to guarantee efficient magnetic seperation. Metallic gold could be facilely recovered from wastewaters containing Au(III).
