Structure and photocatalytic performance of rice husk-like Ba-doped GaOOH under light irradiation

Abstract

The effects of Ba-doping on the structure and photocatalytic performance of GaOOH were investigated for the first time in this paper. XRD, SEM, TEM, XPS, UPS, FT-IR, UV-Vis DRS, PL, BET and EPR characterizations were carried out to analyze the properties of Ba-doped GaOOH. The results showed that GaOOH crystallized well with the orthorhombic crystal system with space group Pbnm. The lattice parameters of GaOOH were found to be a = 4.509526 Å, b = 9.771034 Å and c = 2.969284 Å. The transition in the structural morphology of GaOOH before and after Ba-doping was observed in SEM pictures in which the morphology of GaOOH varied from wood-like to rice husk-like. At the same time, the specific surface area of 4 wt% Ba-doped GaOOH (21.5854 m² g^-1) was 3.42 times that of pure GaOOH (6.3047 m² g^-1). Ba-doping caused a red shift of the band gap according to UV-Vis DRS results. The enhanced defect states caused by Ba-doping was confirmed by PL results, which decreased the recombination rate of photogenerated electrons and photogenerated holes. Compared with pure GaOOH, when GaOOH with different Ba content was used as photocatalyst, the removal rate of enrofloxacin was increased by more than 20% only by illumination for 60 min. In addition, Ba-doped GaOOH had excellent stability and could be reused, which could reduce costs and increase the potential of its practical application.

Fig. 1. XRD patterns and Pawley refinements of: (a) pure GaOOH; (b) 4 wt% Ba-doped GaOOH; (c) 8 wt% Ba-doped GaOOH; (d) 16 wt% Ba-doped GaOOH.

Fig. 2. SEM photographs of: (a) pure GaOOH; (b) 4 wt% Ba-doped GaOOH; (c) 8 wt% Ba-doped GaOOH; (d) 16 wt% Ba-doped GaOOH.

Fig. 3. The high resolution TEM pictures, the selected area electron diffraction (SAED) patterns and the HRTEM images with clear lattice fringe spacing for pure GaOOH (a and b) and 4 wt% Ba-doped GaOOH (c and d).

Fig. 4. XPS spectra of 4 wt% Ba-doped GaOOH ((a) Ba3d; (b) Ga3d; (c) O1s) and (d) FT-IR spectra of pure GaOOH and GaOOH with different Ba-doping amount.

Fig. 5. UV-vis DRS spectra and band gaps of pure GaOOH and GaOOH with different Ba-doping amount.

Fig. 6. (a and b) UPS spectra of pure GaOOH and 4 wt% Ba-doped GaOOH; (c) band structures of pure GaOOH and 4 wt% Ba-doped GaOOH; (d) PL spectra of pure GaOOH and GaOOH with different Ba-doping amount.

Fig. 7. (a) UV-Vis absorption spectra of different concentrations of enrofloxacin; (b) absorbency standard curve of enrofloxacin.

Fig. 8. (a) Removal of enrofloxacin by different photocatalysts with initial pH value of 7; (b) removal of enrofloxacin at different initial pH using 4 wt% Ba-doped GaOOH as a photocatalyst; (c) removal of enrofloxacin with the addition of different capture agents using 4 wt% Ba-doped GaOOH as a photocatalyst; (d) cyclic photocatalytic degradation of enrofloxacin using 4 wt%, 8 wt% and 16 wt% Ba-doped GaOOH as a photocatalyst, respectively.

Fig. 9. DMPO spin-trapping EPR spectra of 4 wt% Ba-doped GaOOH in aqueous dispersion for DMPO–·OH (a) and in methanol dispersion for DMPO–·O₂⁻ (b).