CoO, NiO or CuO oxides were employed as co-catalysts on Bi₂O₃–TiO₂ (BT) structure in the photocatalytic reduction of 4-nitrophenol under UV light irradiation. The intimate contact between the co-catalysts and base material contributed to an enhancement in the photocatalytic activity due to the formation of the p-n heterojunction that effectively separates charge carriers. CuO–BT, NiO–BT and Co–BT showed a reduction of 4-nitrophenol of 83%, 59% and 52% after 60 min under illumination, respectively, which are higher than that obtained with the BT semiconductor. The co-catalysts increase the donor density favoring the reduction of 4-nitrophenol. The donor density calculated for CuO–BT, NiO–BT and Co–BT was of N_d = 15.5 × 10¹⁸ cm⁻³, N_d = 12.4 × 10¹⁸ cm⁻³ and N_d = 9.41 × 10¹⁸ cm⁻³, respectively. The results were associated to that CuO and NiO oxides are considered as reduction co-catalysts while CoO oxide is used as oxidation co-catalyst.

CoO，NiO或CuO氧化物被用作Bi ₂ O ₃ -TiO ₂（BT）结构上的助催化剂，在紫外光照射下光催化还原4-硝基苯酚。助催化剂和基础材料之间的紧密接触由于形成了有效分离电荷载流子的pn异质结而有助于提高了光催化活性。CuO–BT，NiO–BT和Co–BT在光照60分钟后的4-硝基苯酚减少量分别为83％，59％和52％，这比BT半导体所获得的要高。助催化剂增加供体密度，有利于4-硝基苯酚的还原。计算得出的CuO–BT，NiO–BT和Co–BT的供体密度为N _d  = 15.5×10¹⁸  cm ^-3，N _d ＝ 12.4×10 ¹⁸  cm ^-3，N _d ＝ 9.41×10 ¹⁸  cm ^-3。结果与将CuO和NiO氧化物视为还原助催化剂，而CoO氧化物用作氧化助催化剂有关。