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In multiuser visible light communication (VLC) systems, many transmit precoding (TPC) techniques have been investigated to suppress multiuser interference. However, these conventional works restrict their modulation to the special case of zero mean, which inherently limits their application to some popular modulations associated with the non-zero mean in VLC, such as pulse position modulation (PPM). Since the modulation with non-zero mean leads to more intricate optical power constraints and design objective functions than the case of zero mean, the TPC design that can support a general modulation is still an open problem. In the paper, we conceive of a general solution of the TPC scheme combined with dimming control for multiuser VLC systems, which is capable of mitigating multiuser interference, while at the same time, achieving the desired dimming level. The proposed scheme is applicable to a wide range of modulations in VLC, such as pulse amplitude modulation (PAM), PPM, and so on. Simulation results demonstrate that the proposed scheme outperforms the traditional pseudo-inverse-based zero-forcing TPC in terms of bit error rate (BER). [ABSTRACT FROM AUTHOR]

Quantum dots (QDs), a class of promising candidates for harvesting visible light, generally exhibit low activity and selectivity towards photocatalytic CO2 reduction. Functionalizing QDs with metal complexes (or metal cations through ligands) is a widely used strategy for improving their catalytic activity; however, the resulting systems still suffer from low selectivity and stability in CO2 reduction. Herein, we report that doping CdS QDs with transition‐metal sites can overcome these limitations and provide a system that enables highly selective photocatalytic reactions of CO2 with H2O (100 % selectivity to CO and CH4), with excellent durability over 60 h. Doping Ni sites into the CdS lattice leads to effective trapping of photoexcited electrons at surface catalytic sites and substantial suppression of H2 evolution. The method reported here can be extended to various transition‐metal sites, and offers new opportunities for exploring QD‐based earth‐abundant photocatalysts. Quantum dots (QDs), a class of promising nanoparticles for visible‐light harvesting, commonly possess low activity and selectivity towards photocatalytic CO2 reduction. Doping CdS QDs with transition‐metal cations, which can trap photoexcited electrons and suppress H2 evolution, provides an approach to visible‐light‐driven highly selective CO2 reduction with excellent durability. [ABSTRACT FROM AUTHOR]

Abstract: CdS nanocrystals (NCs) is a very important visible-light-driven photocatalyst due to their optimal band gap of 2.4 eV, but their photocatalytic performance is still restrained by a few factor such as easy aggregation and weak response to UV light. In this work, we employ spindle-like GdBO3:Ce,Tb particles as seeds to grow some CdS NCs on their surface. In the prepared GdBO3:Ce,Tb/CdS composite photocatalysts, the GdBO3:Ce,Tb particles not only serve as a substrate to improve the stability of CdS NCs but also work as a light-transducer to convert the UV light to visible emissions to activate the CdS NCs. In contrast to pure CdS NCs, the hybrid photocatalyst exhibit an enhanced photocatalytic performance due to the additional utilization of the UV light and the substrate effect. The hybrid photocatalysts have been characterized by XRD, TEM, and PL etc. and their working mechanism has been elucidated.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Conventional optical orthogonal frequency division multiplexing (OFDM) schemes, such as adaptively biased optical OFDM (ABO-OFDM) and hybrid asymmetrically clipped optical OFDM (HACO-OFDM), are unable to tap all the resources of the subcarriers and only achieve relatively high power efficiency. In this paper, a hybrid adaptive bias optical OFDM (HABO-OFDM) scheme for visible light communication (VLC) is proposed to improve spectral efficiency and power efficiency. In the proposed HABO-OFDM scheme, different optical OFDM components are combined for transmission at the same time, and the adaptive bias is designed to ensure the non-negativity, as well as obtaining significantly high power efficiency. Meanwhile, the implementation complexity of the HABO-OFDM receiver is notably lower than the conventional superimposed optical OFDM schemes. Simulation results show that the proposed HABO-OFDM scheme outperforms ABO-OFDM and HACO-OFDM in terms of both peak-to-average-power ratio (PAPR) and power efficiency. The PAPR performance of HABO-OFDM is about 3.2 dB lower than that of HACO-OFDM and 1.7 dB lower than that of ABO-OFDM. Moreover, we can see that the E b (e l e c) / N 0 required for HABO-OFDM to reach the BER target is lower than the other two schemes at the Bit rate/Normalized bandwidth range of 3.5 to 8.75, which means that the power efficiency of HABO-OFDM is higher in this range. [ABSTRACT FROM AUTHOR]

The development of simple and efficient visible light photocatalytic catalysts for hydrogen production from water is an important development direction in the field of photocatalysis, and composite two-dimensional materials are found to be promising candidates. This paper constructs a novel two-dimensional MoSe 2 /PtSe 2 type-II heterojunction and systematically studies its geometric structure, electronic structure, and optical properties by first-principles calculation. It is evident that the heterojunction has good thermodynamic, kinetic, and mechanical stability, as well as excellent hole carrier mobility, which is conducive to the separation of photogenerated electrons and holes. The optical properties show that MoSe 2 /PtSe 2 heterojunction has the best optical absorption efficiency for visible light and has the ability to cross the water-cracking oxidation-reduction potential at pH = 4. More importantly, the MoSe 2 /PtSe 2 heterojunction shows great hydrogen absorption reaction performance, indicating that it is a potential photocatalyst for overall water splitting of visible light, and has broad application prospects in the field of photocatalysis and optoelectronics. [Display omitted] • The design of a novel type-II MoSe 2 /PtSe 2 heterojunction. • MoSe 2 /PtSe 2 heterostructure can drive overall water splitting at pH = 4. • Thermodynamic feasibilities of HER and OER are confirmed by the Gibbs free energies. • This work broadens the field of vision for the preparation of highly efficient photocatalysts. [ABSTRACT FROM AUTHOR]

Nickel-doped zinc oxide hollow nanospheres have been synthesized using a simple solvothermal approach through a morphological transformation driven by a localized Ostwald ripening process. The saturation magnetization of the system shows that the materials have only a short-range magnetic ordering in them. Based on the visible-light photocatalytic experiment, we could confirm that, with a high doping content (10 mol%), the doping accompanied with increased recombination which reduced the energy of photoinduced electron leading to suppressed photocatalytic activity. Changing reaction parameters, i.e. the mixed reactant concentration, doping content, and different solvents, Zn 1− x Ni x O powders exhibited the elongated prismatic form with sharp tips, quasi-spherical structure, and hexagonal-based polyhedron, respectively. The photocatalytic results demonstrate that different crystal growth orientations, specific surface areas, particle size distributions, and doping levels have strong influences on the photocatalytic activity performances. Among the samples, hexagonal-based polyhedrons have the best photodegradation efficiency standing on higher fraction of exposed polar facets, larger specific surface area, as well as an optimal doping level. The 1 mol% nickel content showed the best photocatalytic activities among the nickel-doped zinc oxide samples. [ABSTRACT FROM AUTHOR]

α-Fe 2 O 3 nanoparticles-decorated ZnO nanorod-assembled hollow spheres were successfully synthesized by a simple acetone-assisted impregnation deposition. SEM images showed a uniform distribution of α-Fe 2 O 3 nanoparticles not only on the surfaces of ZnO spheres but also inside pores of ZnO parallel aligned nanorods. The α-Fe 2 O 3 /ZnO binary semiconductor composites exhibited a superior visible-light photocatalytic activity for degradation of rhodamine B (RhB) as compared with pure ZnO spheres. The enhancement was attributed to stronger visible light absorption ability and effective photogenerated charge separation of α-Fe 2 O 3 /ZnO composites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Six possible stacking patterns of the PtSe 2 /hBNC vdW heterojunction are studied. • PtSe 2 /hBNC has good thermodynamic, kinetic and mechanical stability. • Type-Ⅱ heterojunction has effectively enhanced the photocatalytic activity. • PtSe 2 /hBNC possesses marvelous carrier mobility and OER efficiency. Designing and researching suitable photoelectrocatalyst for water splitting is crucial for the utilization of renewable and inexhaustible solar energy but remains a huge conundrum. Here, using first principles calculations, the two-dimensional PtSe 2 /hBN heterojunction was first conceived. However, the rapid recombination of electrons and holes will inhibit the visible light catalytic efficiency of the heterojunction. In order to realize effective spatial separation of electrons and holes of the heterojunction, we tuned the band gap by doping two carbon atoms on the hBN monolayer to obtain the type-Ⅱ PtSe 2 /hBNC heterojunction. Then through the comprehensive researches on structural, electronic and optical properties, it was found that the structure possesses excellent carrier mobility and exhibits a great oxygen evolution reaction performance with a low overpotential of 0.76 eV, which is an ideal photoelectrocatalyst and exhibits great light absorption performance. In this study, the possible mechanism of doped PtSe 2 /hBNC vdW heterojunction to promote photocatalysis and oxygen evolution ability was explained, which may pave the way for the practical design of more solar-driven high-quality water splitting photoelectrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • hBN/g-C 3 N 4 with six different defected types are constructed and studied in detail. • Z-scheme vdW heterojunctions can realize stronger redox capacity. • A suitable band gap width can even obtain full visible light response. • Defect-engineered can increase even more than 20 times the charge transfer between layers. 2D/2D hBN/g-C 3 N 4 nanocomposites with good photocatalytic activity have been successfully prepared, and fortunately defected 2D material heterojunction opens up new possibilities for high-efficiency photocatalysts. However, its photocatalytic performance and mechanism in splitting water have not been thoroughly explored. Herein, using the state-of-theart TDHF-HSE06 method, 2D/2D hBN/g-C 3 N 4 nanocomposites with different defected types were discussed in detail, including C atoms doping and natural point vacancies. We demonstrate that the defect-induced Z-scheme vdW heterojunction is a key for excellent photocatalytic performance. Compared to perfect hBN/g-C 3 N 4 , the defected hBN/g-C 3 N 4 heterojunctions have stronger interfacial interaction with more than 20 times of charge transfer. And it even has full visible-light response due to the suitable band gap width. More importantly, the Z-scheme band edge potentials have perfect redox capacity for water splitting at both PH = 0 and 7. The findings not only explain the existing experimental phenomena, but also provide new insights into the design of high-efficiency metal-free photocatalysts. [ABSTRACT FROM AUTHOR]

A CdS/MoS 2 photocatalyst was fabricated via a facile photodeposition method for efficient H 2 generation. • MoS 2 is directly grown onto the CdS QD by a facile photodeposition method. • The intimate interfacial contact promotes the charge transfer between CdS and MoS 2. • The MoS 2 provide abundant catalytic sites for CdS QDs towards H 2 evolution. • The CdS/MoS 2 composites exhibit excellent catalytic performance. Photocatalytic hydrogen (H 2) production from water is an appealing approach to alleviate the ever-increasing fossil fuel crisis. The development of visible-light-driven photocatalytic system is an essential task for H 2 generation. CdS quantum dots (QDs) are excellent candidate for photocatalytic H 2 generation. However, the photocatalytic performance of CdS QDs is largely limited by serious charge recombination and photocorrison problems. Herein, we developed a facile method for photodeposition of MoS 2 onto CdS QDs. The in-suit photodeposition approach enables thin-layered MoS 2 to be intimately decorated onto the CdS QD surface. The intimate contact favors the formation of junctions between CdS and MoS 2 , thus promoting charge separation in CdS/MoS 2. Furthermore, the MoS 2 catalysts can provide highly active catalytic sites for H 2 evolution and serve as protective layer for CdS to restrict photocorrison. The resulted CdS/MoS 2 photocatalysts exhibit excellent catalytic activity: the H 2 generation rate reaches 13129 μmol h−1 g−1, which is 7.2 times higher than that of the pristine CdS-S QDs. The CdS/MoS 2 photocatalysts also possess superior photocatalytic durability under visible light. This work provides a novel method for in-suit growth of MoS 2 onto QDs. The surface modification strategy presented here offers new opportunities for developing new-types of photocatalysts based on QDs. [ABSTRACT FROM AUTHOR]