Preparation And Research Of New Type Visible-light Active Photocatalyst BIVO4

Bismuth vanadate (BiVO₄) has three main crystal phases: a zircon structure with a tetragonal (z-t) system and a scheelite structure with a monoclinic (s-m) and a tetragonal (s-t) system, of which only s-mBiVO₄ with bandgap of 2.4ev can be excited by visible light. Traditional photocatalyst TiO2 has an obvious disadvantage that it can only absorb UV-light, so visible light active s-mBiVO₄ receives more and more attention. Compared with s-mBiVO₄, the other two phases show bad photocatalytic performance under visible light, so synthesis of s-mBiVO₄ and its modification are paid more respect. In this paper, key work is to prepare carbon dopped BiVO₄ and new method to synthesis s-mBiVO₄ with large surface area (BET).Using medical absorbent cotton as carbon source, carbon doped s-mBiVO₄ was successfully sythesised through a facile dipping-combustion method. On the basis of the method, the effect of different sintering temperatures to the doping quantity and bandgaps are carried out. From the results, we can see the dopping quantity of carbon increases with the the sintering temperature going up from 500℃to 650℃, but the dopping quantity decreases when the sintering temperature go on increasing to 750℃. The reason for this can be attributed to the competition between carbon doping and carbon combustion. At the same time, energy band gaps of the products change with the quantity of carbon. In order to testify photocatalytic activity of the catalysts, we make RhB target. After irradiated for 2 hours under the visible light (wavelength>420nm), photocatalytic performance of carbon-doped BiVO₄ shows better than that of the traditional solide state reaction product (SSR), and the narrower of the band gap of the photocatalyt, the better of the photocatalytic performance. In this paper, the best photo-degadation rate of the catalyst which holds the narrowest band gap reaches 12 times than SSR product.In order to develop new synthesis method, using ethylene glycol (EG) as solvent and soft template, we successfully synthesized BiVO₄ with large surface area through chemical bath-combustion. Afterwards, the precursor was calcined in a muffle oven at different temperatures (sintering temperature 400℃and 500℃) to produce the porous BiVO₄ nanomaterials. Through a series of characteristic methods of XRD, FESEM, BET and FT-IR, we can see that the products prepared are interconnected porous, and the photocatalyst synthesized under the condition of 7 days (holding time) and 400℃(sintering temperature) owns large surface area (13.29m²Â·g^-1) which is lager than that of SSR product. The photocatalytic test shows the 80% RhB has been degraded in 4 hours under visible light irradiation.Based on a series of characteristic results, the mechanisms for interconnected porous structure is proposed.