A new type of Gd2BiTaO7 nanocatalyst (GBT) was synthesized by a high-temperature solid-phase method, and a heterojunction photocatalyst, which was composed of GBT and silver phosphate (AP), was prepared by the facile in-situ precipitation method for the first time. The photocatalytic property of GBT or the Ag3PO4/Gd2BiTaO7 heterojunction photocatalyst (AGHP) was reported. The structural properties of GBT and AGHP were characterized by an X-ray diffractometer, scanning electron microscope–X-ray energy dispersive spectra, an X-ray photoelectron spectrograph, a synchrotron-based ultraviolet photoelectron spectroscope, a Fourier transform infrared spectrometer, an UV-Vis diffuse reflectance spectrophotometer and an electron paramagnetic resonance spectrometer. The results displayed that GBT was well crystallized with a stable cubic crystal system and space group Fd3m. The lattice parameter or band gap energy of GBT was found to be a = 10.740051 Å or 2.35 eV, respectively. After visible light irradiation of 30 min, the removal rate of bisphenol A (BPA) reached 99.52%, 95.53% or 37.00% with AGHP as the photocatalyst, with Ag3PO4 and potassium persulfate (AP-PS) as photocatalysts or with N-doped TiO2 (NT) as a photocatalyst, respectively. According to the experimental data, it could be found that the removal rate of BPA with AGHP as a photocatalyst was 2.69 times higher than that with NT as a photocatalyst. AGHP showed higher photocatalytic activity for photocatalytic degradation of BPA under visible light irradiation compared with GBT or AP-PS or NT. The removal rate of total organic carbon (TOC) was 96.21%, 88.10% or 30.55% with AGHP as a photocatalyst, with AP-PS as photocatalysts or with NT as a photocatalyst after visible light irradiation of 30 min. The above results indicated that AGHP possessed the maximal mineralization percentage ratio during the process of degrading BPA compared with GBT or AP-PS or NT. The results indicated that the main oxidation radical was •OH during the process of degrading BPA. The photocatalytic degradation of BPA with AGHP as a photocatalyst conformed to the first-order reaction kinetics. This study provided inspiration for obtaining visible light-responsive heterojunction photocatalysts with high catalytic activity and efficient removal technologies for organic pollutants and toxic pollutants, and as a result, the potential practical applications of visible light-responsive heterojunction photocatalysts were widened. The subsequent research of thin-film plating of the heterojunction catalysts and the construction of complete photoluminescent thin-film catalytic reaction systems, which utilized visible light irradiation, could provide new technologies and perspectives for the pharmaceutical wastewater treatment industry.

Originally, the new catalyst Bi2SmSbO7 was synthesized by the hydrothermal synthesis method or by the solid-phase sintering method at a lofty temperature. A solvothermal method was utilized to prepare a Bi2SmSbO7/ZnBiYO4 heterojunction photocatalyst (BZHP). The crystal structure of Bi2SmSbO7 belonged to the pyrochlore structure and face-centered cubic crystal system by the space group of Fd3m. The cell parameter a was equivalent to 10.835(1) Å (Bi2SmSbO7). With Bi2SmSbO7/ZnBiYO4 heterojunction (BZH) as the photocatalyst, the removal rate (RR) of direct orange (DO) and the total organic carbon were 99.10% and 96.21% after visible light irradiation of 160 min (VLI-160M). The kinetic constant k toward DO concentration and visible light irradiation time (VLI) with BZH as photocatalyst reached 2.167 min−1. The kinetic constant k, which was concerned with total organic carbon, reached 0.047 min−1. The kinetic curve that came from DO degradation with BZH as a catalyst under VLI conformed to the second-order reaction kinetics. After VLI-160M, the photocatalytic degradation (PD) removal percentage of DO with BZH as the photocatalyst was 1.200 times, 1.268 times or 3.019 times that with Bi2SmSbO7 as the photocatalyst, ZnBiYO4 as the photocatalyst or with nitrogen-doped titanium dioxide as the photocatalyst. The photocatalytic activity (PA) was as following: BZH > Bi2SmSbO7 > ZnBiYO4 > nitrogen-doped titanium dioxide. After VLI-160M for three cycles of experiments with BZH as the photocatalyst, the RR of DO reached 98.03%, 96.73% and 95.43%, respectively, which meant that BZHP possessed high stability. By using the experiment of adding a trapping agent, the oxidative purifying capability for degradation of direct orange, which was in gradual depressed order, was as following: hydroxyl radical > superoxide anion > holes. Finally, the possible degradation pathway and degradation mechanism of DO were discussed systematically. A new high active heterojunction catalyst BZHP, which could efficiently remove toxic organic pollutants such as DO from dye wastewater after VLI, was obtained. Our research was meant to improve the photocatalytic property of the single photocatalyst.

In2YSbO7 and In2YSbO7/BiSnSbO6 heterojunction photocatalyst were prepared by a solvothermal method for the first time. The structural characteristics of In2YSbO7 had been represented. The outcomes showed that In2YSbO7 crystallized well and possessed pyrochlore constitution, a stable cubic crystal system and space group Fd3m. The lattice parameter of In2YSbO7 was discovered to be a = 11.102698 Å and the band gap energy of In2YSbO7 was discovered to be 2.68 eV, separately. After visible-light irradiation of 120 minutes (VLGI-120M), the removal rate (ROR) of indigo carmine (IC) reached 99.42% with In2YSbO7/BiSnSbO6 heterojunction (IBH) as a photocatalyst. The ROR of total organic carbon (TOC) reached 93.10% with IBH as a photocatalyst after VLGI-120M. Additionally, the dynamics constant k which was taken from the dynamic curve toward (DCT) IC density and VLGI time with IBH as a catalyst reached 0.02950 min−1. The dynamics constant k which came from the DCT TOC density and VLGI time with IBH as a photocatalyst reached 0.01783 min−1. The photocatalytic degradation of IC in dye wastewater (DW) with IBH as a photocatalyst under VLGI was in accordance with the first-order kinetic curves. IBH was used to degrade IC in DW for three cycles of experiments under VLGI, and the ROR of IC reached 98.74%, 96.89% and 94.88%, respectively, after VLGI-120M, indicating that IBH had high stability. Compared with superoxide anions or holes, hydroxyl radicals possessed the largest oxidative ability for removing IC in DW, as demonstrated by experiments with the addition of trapping agents. Lastly, the probable degradation mechanism and degradation pathway of IC were revealed in detail. The results showed that a visible-light-responsive heterojunction photocatalyst which possessed high catalytic activity and a photocatalytic reaction system which could effectively remove IC in DW were obtained. This work provided a fresh scientific research idea for improving the performance of a single catalyst.

A new photocatalyst In2CdO4 was prepared by a solid phase sintering synthesis method at high temperature for the first time in this paper. The In2CdO4/Y2SmSbO7 heterojunction (IYH) catalyst was prepared by the solvent thermal method for the first time. The Y2SmSbO7 compound crystallized in the pyrochlore-type architecture and cubelike crystal system, and the space group of Y2SmSbO7 was Fd3m and the crystal cell parameters of Y2SmSbO7 was 9.51349 Å. The band gap width of Y2SmSbO7 was 2.63 eV. In2CdO4 crystallized with a body centered tetragonal lattice structure which was a tetragonal crystal system with a space group of I41/amd. The band gap width of In2CdO4 was 2.70 eV. After 110 minutes of visible light irradiation (VLGI-110min) with IYH as the photocatalyst, the removal rate (RR) of rhodamine B (RhB) concentration was 100% and the total organic carbon (TOC) concentration RR was 99.71%. The power mechanics invariable k toward RhB consistency and visible light irradiation (VLGI) time with IYH as the photocatalyzer reached 0.03073 min−1. The power mechanics invariable k which was involved with TOC reached 0.03621 min−1. After VLGI-110min, the RR of RhB with IYH as the photocatalyzer was 1.094, 1.174 or 1.740 times higher than that with In2CdO4, Y2SmSbO7 or N-doping TiO2 (N-TO) as the photocatalyzer, respectively. The results showed that the photocatalytic activity of IYH was the highest compared with In2CdO4, Y2SmSbO7, or N-TO. With appending a trapping agent, the oxidative capability for degrading RhB, which ranged from strong to weak among three oxidative radical groups, was as follows: hydroxyl radicals > superoxide anion > holes. This work provided a scientific basis for the research which resulted in prosperous development of efficient heterojunction compound catalysts.

A new photocatalyst, Er2FeSbO7, was prepared by solid phase sintering using the high-temperature synthesis method for the first time in this paper. Er2FeSbO7/BiTiSbO6 heterojunction (EBH) catalyst was prepared by the solvent thermal method for the first time. Er2FeSbO7 compound crystallized in the pyrochlore-type architecture and cubelike crystal system; the interspace group of Er2FeSbO7 was Fd3m and the crystal cellular parameter a of Er2FeSbO7 was 10.179902 Å. The band gap (BDG) width of Er2FeSbO7 was 1.88 eV. After visible light irradiation of 150 minutes (VLGI-150min) with EBH as a photocatalyst, the removal rate (RR) of enrofloxacin (ENR) concentration was 99.16%, and the total organic carbon (TOC) concentration RR was 94.96%. The power mechanics invariable k toward ENR consistency and visible light irradiation (VLGI) time with EBH as a photocatalyzer attained 0.02296 min−1. The power mechanics invariable k which was involved with TOC attained 0.01535 min−1. The experimental results showed that the photocatalytic degradation (PCD) of ENR within pharmaceutical waste water with EBH as a photocatalyzer under VLGI was in keeping with the single-order reactivity power mechanics. The RR of ENR with EBH as a photocatalyzer was 1.151 times, 1.269 times or 2.524 times that with Er2FeSbO7 as a photocatalyst, BiTiSbO6 as a photocatalyst, or N-doping TiO2 (N-TO) as a photocatalyst after VLGI-150min. The photocatalytic activity, which ranged from high to low among above four photocatalysts, was as follows: EBHP > Er2FeSbO7 > BiTiSbO6 > N-TO. After VLGI-150min toward three periods of the project with EBH as a photocatalyst, the RR of ENR attained 98.00%, 96.76% and 95.60%. The results showed that the stability of EBH was very high. With appending trapping agent, it could be proved that the oxidative capability for degrading ENR, which ranged from strong to weak among three oxidic radicals, was as follows: superoxide anion > hydroxyl radicals (HRS) > holes. This work provides a scientific basis for the research and oriented leader development of efficient heterojunction catalysts.