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In the past seven years, dual Z-scheme heterojunctions evolved as favorable approaches for enhanced charge carrier separation through direct or indirect charge transfer transportation mechanisms. The dynamics of the charge transfer is the major strategy for understanding their photoactivity and stability through the formation of distinctive redox centers. The understanding of currently recognized principles for successful fabrication and classification in different energy and pollution remediation strategies is discussed, and a universal charge transfer-type-based classification of dual Z-schemes that can be adopted for Z-scheme and S-scheme heterojunctions is proposed. Methods used for determining the charge transfer as proof of dual Z-scheme existence are outlined. Most importantly, a new macroscopic N-scheme and a triple Z-scheme that can also be adopted as triple S-scheme heterostructures composed of four semiconductors are proposed for generating both oxidatively and reductively empowered systems. The proposed systems are expected to possess properties that enable them to harvest solar light to drive important chemical reactions for different applications.

Remediation of organic pollutant matrixes from wastewater by photodegradation using different heterojunctions is extensively studied to improve performance for potential application. Brilliant black (BB) and p -nitrophenol (PNP) have been detected in the environment and implicated as directly or indirectly carcinogenic to human health. This work analyzes their elimination from aqueous solutions under visible-light irradiation with composites of cobalt(II, III) oxide and bismuth oxyiodides (Co 3 O 4 /Bi 4 O 5 I 2 /Bi 5 O 7 I). The synthesized nanomaterial properties were investigated using various techniques such as BET, SEM/EDS, TEM, XRD, FTIR, PL, and UV–vis. All the nanocomposites absorbed in the visible range of the solar spectrum with band gaps between 1.68 and 2.79 eV, and the specific surface area of the CB2 composite increased by 35.8% from that of Bi 4 O 5 I 2 /Bi 5 O 7 I. There was an observed massive reduction in the rate of electron and hole recombination, and the band gaps of the composites decreased. The mineralization of PNP and BB was followed by determination of the total organic carbon with reductions of 93.6 and 83.7%, respectively. The main active species were the hydroxyl radicals, while the superoxide anion radical and generated holes were minor as confirmed by radical trapping experiments. The optimum pHs for degradation of PNP and BB were 9.6 and 5.3, respectively. The enhanced performance of the catalyst was due to C-scheme heterojunction formation that reduced the electron and hole recombination rate and was attributed to strong adsorption of the pollutants on the photocatalyst active surface. The nanocomposite is apposite for solar energy-driven remediation of organic pollutants from environmental aqueous samples.

Environmental pollution is regarded as a major concern and photocatalysis has been used successfully to combat discharges of recalcitrant pollutants. In this study, meso tetraphenylporphyrin (TPP), tungsten (VI) oxide and reduced graphene oxide nanocomposite materials were prepared by in situ method and calcined at different temperatures. The catalysts impact was evaluated for the degradation of acid blue 25 (AB25) under visible light irradiation. The as‐prepared composite materials were characterised for morphological and crystalline structural properties using SEM, Raman, FTIR, TGA, BET and XRD techniques. UV‐Vis and PL absorption studies obtained a band gap energy of 2.14 eV which showed its ability to absorb light in the visible region. The nanocomposite exhibited spherically shaped particles of monoclinic WO3 when using 20 mg TPP and calcination temperature of 350 °C for 4 hours. The highest degradation efficiency of 85% on 20 ppm AB25 as per UV/Vis and TOC results, was obtained for the photocatalyst calcined at 350 °C for 4 hours. The high degradation efficiency can be ascribed to the visible light absorbing nature of the composite and high separation rate of photogenerated charge carriers. This nanocomposite can be a suitable candidate for treatment of other dyestuff in textile effluents.

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