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A self-stabilized Z-scheme porous g-CN/I-containing BiOI ultrathin nanosheets (g-CN/I-BiOI) heterojunction photocatalyst with I/I redox mediator was successfully synthesized by a facile solvothermal method coupling with light illumination. The structure and optical properties of g-CN/I-BiOI composites were systematically characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, N adsorption/desorption, UV-vis diffuse reflectance spectrum, and photoluminescence. The g-CN/I-BiOI composites, with a heterojunction between porous g-CN and BiOI ultrathin nanosheets, were first applied for the photocatalytic elimination of ppm-leveled CHSH under light-emitting diode visible light illumination. The g-CN/I-BiOI heterojunction with 10% g-CN showed a dramatically enhanced photocatalytic activity in the removal of CHSH compared with pure BiOI and g-CN due to its effective interfacial charge transfer and separation. The adsorption and photocatalytic oxidation of CHSH over g-CN/I-BiOI were deeply explored by in situ diffuse reflectance infrared Fourier transform spectroscopy, and the intermediates and conversion pathways were elucidated and compared. Furthermore, on the basis of reactive species trapping, electron spin resonance and Mott-Schottky experiments, it was revealed that the responsible reactive species for catalytic CHSH composition were h, O, and O; thus, the g-CN/I-BiOI heterojunction followed an indirect all-solid state Z-scheme charge-transfer mode with self-stabilized I/I pairs as redox mediator, which could accelerate the separation of photogenerated charge and enhance the redox reaction power of charged carriers simultaneously.

Non-orthogonal multiple access (NOMA) has recently attracted significant attention as a promising multiple access scheme for the 5th generation (5G) wireless communication due to its superior spectral efficiency, which has also been studied and shown to achieve a superior performance in visible light communication (VLC) networks. However, the error propagation (EP) problem due to successive interference cancellation (SIC) decoding has not yet been resolved, which degrades the system BER performance and causes user unfairness. In this work, symmetric superposition coding (SSC) and symmetric SIC (SSIC) decoding are proposed for a downlink NOMA-based VLC network, in which the distribution of the demodulation regions of the user allocated with more power will be symmetrical in terms of the decision threshold of the user allocated with less power. Furthermore, the proposed method is experimentally tested and the results show that more than 90% demodulation errors caused by EP are eliminated compared with traditional NOMA VLC.

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