Synthesis of noble‐metal‐free ternary K₇HNb₆O₁₉/Cd_0.5Zn_0.5S/g‐C₃N₄ tandem heterojunctions for efficient photocatalytic performance under visible light

Abstract

Exploring noble-metal-free, highly active and durable catalysts is vital to get to grips with the energy and environmental issues. Herein, we first dexterously design and synthesize a class of ternary Nb 6 /CZS/g-CN photocatalysts for the removal of hexavalent chromium Cr (VI) and organic dye pollutant (MO) from wastewater under visible-light irradiation. A heterojunction Nb 6 -1/CZS/g-CN loaded with 0.01 g K 7 HNb 6 O 19 showed excellent photocatalytic performance, with the MO photodegradation efficiency of 94% in 1 h and the Cr (VI) (150 mg/l) photoreduction efficiency as high as 91% in 2 hr. The main active species were deemed to be O 2 .-. Additionally, the as-prepared ternary heterojunction exhibits superior hydrogen evolution reaction (HER) rate. A heterojunction Nb 6 -4/CZS/g-CN loaded with 0.5 g K 7 HNb 6 O 19 exhibited the highest H 2 evolution rate as high as 1777.86 μmol h −1 g −1 under visible-light illumination, which is increased to 5.7 and 2.7 times that of bare CZS and biphase heterojunction CZS/g-CN . These findings afford a new class of promising low-cost photocatalyst bodying for its huge potential value in sustainable energy development and wastewater treatment.

Binary Type-II Heterojunction K7HNb6O19/g-C3N4: An Effective Photocatalyst for Hydrogen Evolution without a Co-Catalyst

“…To give the further information of the composite photocatalysts, the FT-IR spectra of the K 7 HNb 6 O 19 , g-C 3 N 4 and Nb–CN-0.4 composite were carried out as representatives. As shown in Figure 3 , for Nb–CN-0.4 composite, the three vibrational absorption peaks observed at 853, 674 and 530 cm −1 belonged to the tensile vibration of Nb–O and Nb–O–Nb of K 7 HNb 6 O 19 [ 24 , 36 ]. The characteristic peaks of g-C 3 N 4 in Nb–CN-0.4 appeared at different wavebands in the absorption region.…”

“…The three N 1s peaks in Nb–CN-0.4 composite were observed at the positions 399.8, 400.9 and 401.8 eV, with the intensity slightly greater than those of g-C 3 N 4 , corresponding to the peaks of sp 2 N atoms involved in tris-triazine rings (C=C–N), tertiary nitrogen (N–(C) 3 ) and N atoms bonded with H atoms (C–N–H) in the aromatic rings, respectively [ 44 ]. It can be seen from Figure 6 c that three peaks, centered at 528.9, 530.6 and 531.9 eV, were observed on the K 7 HNb 6 O 19 sample, which were assigned to Nb–O–Nb, Nb–O–H and adsorbed water, respectively [ 24 ]. After hydrothermal treatment, the O 1s in Nb–CN-0.4 had two main peaks, of which the peak at 532.1 eV was adsorbed water, while the other one resulted from the binding energy of different oxygen-containing species.…”

“…After hydrothermal treatment, the O 1s in Nb–CN-0.4 had two main peaks, of which the peak at 532.1 eV was adsorbed water, while the other one resulted from the binding energy of different oxygen-containing species. Compared with the pure K 7 HNb 6 O 19 , the binding energy peaks located at 206.8 and 209.5 eV corresponded to Nb 3d 5/2 and 3d 3/2 in the Nb–CN-0.4 composite, which indicates that Nb is in its highest oxidation state (+5 valence state) [ 24 ] ( Figure 6 d), and the shift of Nd 3d binding energy further confirmed that there was an interaction between the Lindqvist unit of the K 7 HNb 6 O 19 sample and g-C 3 N 4 sample. Figure S6 shows that K 2p binding energies did not change significantly in K 7 HNb 6 O 19 and the composite, except for their intensities.…”

“…Among them, two strategies of loading noble metals and constructing heterojunctions have been employed widely as effective ways to boost the catalytic property of g-C 3 N 4 [ 23 ]. Nevertheless, constructing heterojunctions by combining with other semiconductors is a preferred method to fabricate g-C 3 N 4 -based photocatalysts on account of the high scarcity and cost of noble metals [ 24 ]. It was proven that the combination of g-C 3 N 4 and POMs is an effective strategy to obtain heterojunctions with improved photoactivity, which not only gives them a large specific surface and a narrowed band gap, but also could accelerate the photoinduced interfacial charge transfer and inhibit effectively the recombination of the electrons and holes in the process of photocatalysis.…”

Reversible Thermochromism and Stable Resistance Switching Behaviors Based on a Co(III)-Complex-Linked Polyoxoniobate

“…Polyoxoniobates (PONbs) are the branch of POMs and have drawn great attention due to their diverse structures and broad applications in photocatalysis, chemical warfare agents, nuclear waste treatment, energy storage materials, and biomedical fields . Therefore, more and more researchers are attracted to the research of PONbs. , However, in contrast with other POMs, such as POMos, POTs, and POVs, the research progress of PONbs is relatively slow .…”