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Developing suitable catalysts capable of receiving injected electrons and possessing active sites for hydrogen evolution reaction (HER) is the key to building an efficient dye-sensitized system for hydrogen production. Fe3S4 is generally regarded as an inferior HER catalyst among the metal sulfide family, mainly due to its weak surface adsorption toward H atoms. In this work, we demonstrate a facile metal-organic framework-derived method to synthesize uniform Fe3S4 nanorods and active them for HER by Ni doping. Our experimental results and theoretical calculations reveal that Ni doping can greatly modify the electronic structure of Fe3S4 nanorods, improving their electron conductivity and optimizing their surface adsorption energy toward H atoms. Sensitized by a commercial organic dye (eosin-Y), 1%Ni-doped Fe3S4 nanorods display a high H2 production rate of 3240 μmol gcat-1 h-1 with an apparent quantum yield of 12% under 500 nm wavelength, which is significantly higher than that of pristine Fe3S4 and even higher than that of 1% Pt-deposited Fe3S4. The working mechanism of this dye-sensitized system is explored, and the effect of Ni-doping concentration has been studied. This work presents a facile strategy to synthesize metal-doped sulfide nanocatalysts with greatly enhanced activity toward photocatalytic H2 production.

Photocatalytic reduction of CO2 into value-added chemical fuels is an appealing approach to address energy crisis and global warming. CsPbBr3 quantum dots (QDs) are good candidates for CO2 reduction because of their excellent photoelectric properties, including high molar extinction coefficient, low exciton binding energy, and defect tolerance. However, the pristine CsPbBr3 QDs generally have low photocatalytic performance mainly due to dominant charge recombination and lack of efficient catalytic sites for CO2 adsorption/activation. Herein, we report a new photocatalytic system, in which CsPbBr3 QDs are coupled with covalent triazine frameworks (CTFs) for visible-light-driven CO2 reduction. In this hybrid photocatalytic system, the robust triazine rings and periodical pore structures of CTFs promote the charge separation in CsPbBr3 and endow them with strong CO2 adsorption/activation capacity. The resulting photocatalytic system exhibits excellent photocatalytic activity towards CO2 reduction. This work presents a new photocatalytic system based on CTFs and perovskite QDs for visible-light-driven CO2 reduction, which highlights the potential of perovskite-based photocatalysts for solar fuel applications.

Herein, we investigate the system spectral efficiency (SSE) and system energy efficiency (SEE) for massive two-way multiple-input-multiple-output (MIMO) relaying networks while considering imperfect channel state information (CSI) with $K$ -pair users in the presence of the hybrid relaying processing. First, we obtain the general expression of the signal-to-interference-and-noise-ratio (SINR) for the considered system when the antenna number of the relay station (RS) $M$ tends to be significantly large. Next, we consider the power scaling scheme (PSS) and achieve asymptotic SSE and SEE. We set the pilot sequence transmit power $P_{P}$ to be fixed $P_{P}$ and variable $P_{P}$ . For a nonvanishing SINR, we achieve different power scaling cases under fixed and variable $P_{P}$ . For a fixed $P_{P}$ value, the optimal PSS of the SSE can be obtained when the transmit power of each user can be scaled by $M$ , whereas that of the SEE can be achieved when the transmit power of both the RS and each user terminal can be reduced by $M$ . Based on the variable value of $P_{P}$ , the optimal PSS’ of both the SSE and the SEE can be used when the transmit power of both RS and each user can be scaled by $M^{1/3}$ . Thus, we conclude that the required SSE and SEE performances can be attained in multi-pair massive MIMO two-way relaying networks with a considerably low transmit power at RS and/or the transmit power of each user. The analytical results for the same are validated via simulation.

Photocatalytic CO2 reduction is an appealing approach to convert solar energy into high value-added chemicals. All-inorganic CsPbBr3 quantum dots (QDs) have emerged as a promising photocatalyst for reducing CO2. However, pristine CsPbBr3 has a low catalytic performance, mainly due to severe charge recombination. Herein, a 0D/2D heterojunction of CsPbBr3 QDs/Bi2WO6 nanosheet (CPB/BWO) photocatalysts is fabricated for photocatalytic CO2 reduction. The CPB/BWO photocatalyst achieves excellent photocatalytic performance: the total yield of CH4/CO is 503 μmol g-1, nearly 9.5 times higher than the pristine CsPbBr3. The CPB/BWO heterojunction also exhibits much-improved stability during photocatalytic reactions. On the basis of various characterization techniques, our investigations verified a direct Z-scheme charge migration mechanism between CsPbBr3 QDs and Bi2WO6 nanosheets. The improved photocatalytic performance is originated from the high spatial separation of photoexcited charge carriers in CPB/BWO, which can also preserve strong individual redox abilities of two components. This work reports an efficient direct Z-scheme heterojunction photocatalytic system based on metal halide perovskites. The novel strategy we proposed may bring up new opportunities for the development of metal halide perovskite photocatalysts with greatly enhanced activities.

Photocatalytic CO2 reduction is a promising technology to mitigate global warming and enrich energy supply. Metal–organic frameworks (MOFs) are prospective photocatalysts for CO2 reduction, but severe charge recombination and limited visible light response largely restrain their applications. As carbon dots (CDs) can act as both electron receptors and photosensitizers, here we propose to develop CD-hybridized MOF photocatalysts for improving their activity for CO2 reduction. In particular, because of the small size of CDs, we have managed to encapsulate CDs inside MOF particles and found that these CD@MOFs exhibit hugely improved photocatalytic activity compared with CD-decorated MOFs or pristine MOFs. Our investigations suggest that placing small CD cocatalysts near the internal metal–oxo clusters of MOFs can help efficient charge transfer and separation in the hybrid photocatalysts, due to the formation of many small heterojunctions among MOFs. The developed CD-hybridized MOF catalysts are characterized in detail and their working mechanism is explored. This work may demonstrate a novel strategy to develop MOF-based hybrid photocatalysts with enhanced photocatalytic activity.

Vehicular fog and cloud computing (VFCC) system, which provides huge computing power for processing numerous computation-intensive and delay sensitive tasks, is envisioned as an enabler for intelligent connected vehicles (ICVs). Although previous works have studied the optimal offloading scheme in the VFCC system, no existing work has considered the departure of vehicles that are processing tasks, i.e., the occupied vehicles. However, vehicles leaving the system with uncompleted tasks will affect the overall performance of the system. To solve the problem, in this paper, we study the optimal offloading scheme that considers the departure of occupied vehicles. We first formulate the task offloading problem as an semi-Markov decision process (SMDP). Then we design the value iteration algorithm for the SMDP to maximize the total long-term reward of the VFCC system. Finally, the numerical results demenstrate that the proposed offloading scheme can achieve higher system reward than the greedy scheme.

Harvesting solar energy to convert carbon dioxide (CO2) into fossil fuels shows great promise to solve the current global problems of energy crisis and climate change. To achieve this goal, it is desirable to develop efficient catalysts with visible light response to cater for the solar spectrum. CdTe QDs are ideal candidates for absorbing visible light, but it is difficult to directly perform CO2 reduction due to the lack of effective catalytic sites. Herein, we report a strategy for the activation of mercaptopropionic acid (MPA)-capped CdTe QDs for visible-light-driven CO2 reduction, in which iron ions (Fe2+) are immobilized onto CdTe QDs using L-cysteine as a bridging ligand (CdTe-b-Fe). This ligand bridging strategy can immobilize Fe2+ ions on the surface of CdTe QDs as catalytic sites, and these catalytic sites can be conveniently adjusted by directly adding different types or numbers of metal ions. In addition to effectively immobilizing catalytic sites, the bridging ligands can also provide a pathway for electron transport between CdTe QDs and the catalytic sites. The CdTe-b-Fe QD system based on the ligand bridging strategy exhibits excellent catalytic properties: the yield of CH4/CO (two products together) is 126 μmol g−1 h−1, and the selectivity for carbon-based products approaches 98%. This work presents a facile strategy for immobilizing catalytic sites on QDs and provides a platform for designing efficient visible-light driven catalysts for CO2 reduction.

Nanostructured α-Co(OH)2 materials are promising noble-metal-free electrocatalysts for oxygen evolution reaction (OER), but their performance is severally restrained by their poor conductivity. Combination of α-Co(OH)2 and carbon nanotubes (CNTs) can improve their conductivity, but it is difficult to build sufficient interface contact between them due to the mismatched hydrophobicity. Herein, we demonstrate a facile method to in situ grow α-Co(OH)2 nanosheets (NSs) on graphene nanoribbons (GNRs), an intriguing belt-like conductive material after oxidative unzipping of CNTs. Owing to the rich of functional groups, the GNRs can be utilized as substrate in solution to prepare dispersive α-Co(OH)2 nanosheets on their surface. The developed α-Co(OH)2 NSs are well contact with the conductive GNRs substrate and offer sufficient active surface area, showing obviously better OER performance than the α-Co(OH)2 and CNTs/Co(OH)2 prepared under the same condition. The composite electrocatalysts have been characterized by various apparatuses, and their OER activities are explored in detail.

A novel frequency-dependent wall insertion loss model at 3–6 GHz is proposed in this paper. The frequency-dependence of the wall insertion loss is modeled by the Fourier triangular basis neural network. A method to determine the optimal weighted vector and the number of the neurons is introduced. In addition, the impact of the wider continuous spectrum on the wall insertion loss is analyzed and extensive measurements are performed to validate the proposed model. The results obtained with the proposed model match better with the measured results than other models. The proposed model can be used in future indoor Internet-of-Things applications such as service computing.

This paper assesses the performances of a downlink cooperative non-orthogonal multiple access (C-NOMA) network over Nakagami-m fading channels. The analytical outage probability expression for each user is derived and verified by Monte Carlo simulations. Based upon the outage probability, the maximal throughputs are obtained and analyzed under different channel conditions. Furthermore, the effects of channel fading on the probability and throughput are investigated. The results indicate that the performance of the C-NOMA system is excellent over the source-relay link with less fading. This analysis can be used for designing the C-NOMA systems in the future fifth-generation wireless communication.

The central limit theorem (CLT)-based Gaussian approximation facilitates the probability analysis of cognitive radio (CR), but it incurs data rate loss due to the inaccurate configuration of the optimal sensing duration (OSD). To estimate the data rate loss, an approach to obtain a tight upper bound of the maximal achievable data rate over a Nakagami-m fading via-to-sense channel is proposed. Moreover, a direct formula is more desirable than an iteration scheme for a highly mobile CR that has to calculate the OSD more quickly. To meet this need, a strategy to achieve the OSD based on exponential interpolation is proposed. For Nakagami-Gamma shadowed fading via-to-sense channels, the proposed scheme is demonstrated to have advantages over the popularly utilized Hermite spline, such as: 1) a more tractable derivation of the probability density function (PDF) of the OSD and 2) a less complex calculation of the ergodic-sensing capacity. These advantages are significantly favorable for a CR network to achieve low latency communication and swiftly perform quality of service management to adapt to the high mobility.

A novel closed-form and stochastic internal wall insertion loss model (IWIL) in the indoor- indoor channel is proposed in this paper. The IWIL (dimensionless) is modeled as a generalized beta prime distributed random variable on the basis of the Nakagami fading. The probability distribution function (PDF), expectation, and standard deviation of IWIL are derived based on the proposed model. The impacts of the Nakagami-m parameters on the expectation and standard deviation of IWIL are also analyzed. Extensive IWIL measurements at 3.5, 6, and 11 GHz are carried out to validate the proposed model. Both Kolmogorov- Smirnov and Chi-square tests are exploited to determine the goodness of fitting between the modeled and measured data. Results show that the modeled PDF provides a better fit to the measured PDF than that of the Log-normal distribution. The proposed model can be used for the dense small cell networks in the future fifth generation wireless communication.

Linear precoding algorithms with low complexity in massive multi-in multi-out system have always been a hot research topic to solve the problem of inter-cell interference. In this paper, we proposed a conjugate gradient-based regularized zero-forcing (CG-RZF) precoding algorithm, with which the base station can directly obtain the transmitted signal after RZF precoding and avoid directly solving the inverse matrix in RZF. Moreover, an RZF precoding algorithm based on a parallel conjugate gradient (Parallel-CG-RZF) is also proposed, which can optimize initial values and iterative process of the aforementioned CG-RZF precoding algorithm. The simulation results have shown that the proposed CG-RZF and the optimized Parallel-CG-RZF precoding algorithm can significantly improve the performance of bit error rate with fast convergence speed compared with other precoding algorithms and can reduce the number of global communications. Meanwhile, the calculation complexity of the proposed CG-RZF and Parallel-CG-RZF precoding algorithm is much lower than the optimized Chebyshev iteration algorithm.

Inspired by the distinct advantages of BiOCl(001) ultrathin nanosheets being rich in oxygen vacancies (VO) and metal nanoparticles (NPs) with unique surface activity for the adsorption-activation of alcohols, metal-decorated BiOCl(001) ultrathin nanosheets were expected to exhibit enhanced photocatalysis for the selective oxidation of aromatic alcohols. Herein, a small quantity (1.5 wt%) of Au and Pd NPs were loaded on ultrathin BiOCl(001) nanosheets by photodeposition to obtain Au–BiOCl and Pd–BiOCl photocatalysts, respectively. Among the various photocatalysts including BiOCl ultrathin nanosheets, light-irradiated BiOCl ultrathin nanosheets, and metal-decorated BiOCl ultrathin nanosheets, the Pd–BiOCl sample displayed the highest photocatalytic activity for the oxidation of aromatic alcohols to the corresponding aldehydes under ambient conditions. According to a series of experimental analyses as well as the insights from the calculations, the enhanced photocatalysis of Pd–BiOCl was attributed to the remarkable interface cooperation by the electronic coupling between Pd and the BiOCl(001) surface, where the abundant VO sites of BiOCl(001) ultrathin nanosheets and the surface activity of Pd NPs synergistically promote the adsorption-activation of O2 and alcohol molecules as well as facilitating the separation and transfer of photogenerated carriers. These findings highlight the synergistic effect of the metal–semiconductor interface on the photocatalytic oxidation of organic compounds and shed some light on the rational design of highly efficient photocatalysts for selective conversion processes with environmentally benign oxidants like O2.

Photocatalytic reduction of CO2 into high value-added CH4 is a promising solution for energy and environmental crises. Integrating semiconductors with cocatalysts can improve the activities for photocatalytic CO2 reduction; however, most metal cocatalysts mainly produce CO and H2. Herein, we report a cocatalyst hydridation approach for significantly enhancing the photocatalytic reduction of CO2 into CH4. Hydriding Pd cocatalysts into PdH0.43 played a dual role in performance enhancement. As revealed by our isotopic labeling experiments, the PdH0.43 hydride cocatalysts reduced H2 evolution, which suppressed the H2 production and facilitated the conversion of the CO intermediate into the final product: CH4. Meanwhile, hydridation promoted the electron trapping on the cocatalysts, improving the charge separation. This approach increased the photocatalytic selectivity in CH4 production from 3.2% to 63.6% on Pd{100} and from 15.6% to 73.4% on Pd{111}. The results provide insights into photocatalytic mechanism studies and introduce new opportunities for designing materials towards photocatalytic CO2 conversion.

The construction of a p-n heterojunction is an efficient strategy to resolve the limited light absorption and serious charge-carrier recombination in semiconductors and enhance the photocatalytic activity. However, the promotion effect is greatly limited by poor interfacial charge transfer efficiency as well as reduced redox ability of charge carriers. In this work, we demonstrate that the embedding of metal Pd into the interface between n-type C3N4 and p-type Cu2O can further enhance the interfacial charge transfer and increase the redox ability of charge carriers through the design of the C3N4-Pd-Cu2O stack nanostructure. The embedded Pd nanocubes in the stack structure not only trap the charge carriers from the semiconductors in promoting the electron-hole separation but also act as a Z-scheme "bridge" in keeping the strong reduction/oxidation ability of the electrons/holes for surface reactions. Furthermore, Pd nanocubes also increase the bonding strength between the two semiconductors. Enabled by this unique design, the hydrogen evolution achieved is dramatically higher than that of its counterpart C3N4-Cu2O structure without Pd embedding. The apparent quantum efficiency (AQE) is 0.9% at 420 nm for the designed C3N4-Pd-Cu2O. This work highlights the rational interfacial design of heterojunctions for enhanced photocatalytic performance.

Utilization of visible and near-infrared light has always been the pursuit of photocatalysis research. In this article, an approach is developed to integrate dual plasmonic nanostructures with TiO2 semiconductor nanosheets for photocatalytic hydrogen production in visible and near-infrared spectral regions. Specifically, the Au nanocubes and nanocages used in this work can harvest visible and near-infrared light, respectively, and generate and inject hot electrons into TiO2 . Meanwhile, Pd nanocubes that can trap the energetic electrons from TiO2 and efficiently participate in the hydrogen evolution reaction are employed as co-catalysts for improved catalytic activity. Enabled by this unique integration design, the hydrogen production rate achieved is dramatically higher than those of its counterpart structures. This work represents a step toward the rational design of semiconductor-metal hybrid structures for broad-spectrum photocatalysis.

The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF4:Yb,Tm–BiOCl hybrid structure based on the choice of suitable BiOCl facets in depositing NaYF4:Yb,Tm upconversion nanocrystals. It was found that the selective deposition of NaYF4:Yb,Tm nanocrystals on the BiOCl(110) facet can greatly enhance the photocatalytic performance in dye degradation compared with the sample with NaYF4:Yb,Tm nanocrystals loaded on the BiOCl(001) facet. Two effects were believed to contribute to this enhancement: (1) a stronger UV emission absorption ability of the BiOCl(110) facet from NaYF4:Yb,Tm in generating more photo-induced charge carriers resulted from the narrower bandgap; (2) a shorter diffusion distance of photogenerated charge carriers to the BiOCl(110) reactive facet for surface catalytic reactions owing to the spatial charge separation between different facets. This work highlights the rational interfacial design of an upconversion nanocrystal–semiconductor hybrid structure for enhanced energy transfer in photocatalysis.

High-quality hexagonal NaYF4:Yb,Tm upconversion nanocrystals (UCNs) prepared in organic solutions display uniform sizes and strong UC emissions, but they possess a hydrophobic surface which hinders combining them with various semiconductor nanocrystals (NCs) to form a hybrid NIR-activated photocatalyst. Herein we present a facile approach to modify hydrophobic UCNs with a uniform carbon layer and enable them with hydrophilicity and surface functionalization. The carbon shell provides a good substrate for enriching with metal ions and in situ generation of CdS nanoclusters on the particle surface which can utilize both the upconverted UV and visible emissions. The developed NaYF4:Yb,Tm@C@CdS nanoparticles are characterized with TEM, SEM, XRD, PL and UV-Vis spectra and their formation mechanism is elucidated. The products display good photocatalytic activity under visible light and obviously enhanced performance under Vis-NIR light, due to the efficient utilization of UC emissions and the strong adsorption capacity of the carbon shell. The working mechanism of the hybrid photocatalysts is also proposed.

A NaYF4 host matrix with a new cubic phase is fabricated to offer high upconversion luminescence efficiency. The new cubic phase is formed through a hexagonal-to-cubic phase transition by shining intense near-infrared light on lanthanide-doped hexagonal NaYF4 materials.

Graphitic (g-) C3N4 is a promising visible light-driven photocatatalyst but it has a narrow absorption in the solar spectrum. To broaden its light utilization, here we present a strategy to integrate upconversion nanocrystals into g-C3N4 nanosheets by electrostatic assembly. This hybrid photocatalyst can be activated under both visible and near-infrared (NIR) lights, showing improved photocatalytic activity in the full solar spectrum. Phase, morphology and activity of this composite photocatalyst are characterized and its working mechanism is also proposed.

Because of the limited penetration depth of visible light that generally excites most of the available photosensitizers (PSs), conventional photodynamic therapy (PDT) is limited to the treatment of superficial and flat lesions. Recently, the application of deep penetrating near-infrared (NIR) light excitable upconversion nanoparticles (UCNs) in conjunction with PDT has shown to have clear potential in the treatment of solid tumors due to its ability to penetrate thick tissue. However, various constructs developed so far have certain limitations such as poor or unstable PS loading, reducing their therapeutic efficacy and limiting their application to solution or cell-based studies. In this work, we present a method to fabricate uniform core-shell structured nanoconstruct with a thin layer of photocatalyst or PS-titanium dioxide (TiO2) stably coated on individual UCN core. Our design allows controllable and highly reproducible PS loading, preventing any leakage of PS compared to previously developed nanoconstructs, thus ensuring repeatable PDT results. Further surface modification of the developed nanoconstructs with polyethylene glycol (PEG) rendered them biocompatible, demonstrating good therapeutic efficacy both in vitro and in vivo.

Synthesis of N-doped TiO2 hollow spheres with a small grain size, large surface area and high degree of crystallinity is favorable to achieve an overall high photocatalytic activity. But traditional synthetic approaches generally involve many tedious steps and are time-consuming. Here we present a facile method to synthesize N-doped TiO2 hollow spheres using organic silane-doped silica nanoparticles as templates. The organic–inorganic silica can be simultaneously etched during the deposition of TiO2 shell to create a thin silica layer on the TiO2 surface. Such a thin silica layer can efficiently protect the TiO2 nanocrystals from growing larger during high-temperature calcination. At the same time, the organic silane can serve as a nitrogen source to be doped in the TiO2 shell. The developed silica-protected and N-doped TiO2 hollow spheres can be directly employed as photocatalysts without SiO2 etching and show obvious light utilization in both UV and visible bands.

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.

Uniform and assembled LaBO3 nanocrystals have been successfully synthesized via a facile hydrothermal method. These assemblies exhibit a rod-shape morphology and each of them consists of small LaBO3 nanocrystals which are tightly attached together. The phase, surface and morphology of these assemblies have been characterized. A possible assembly mechanism of such morphology is also proposed through investigation on the formation process. Photoluminescent spectra suggest that these assemblies doped with Eu3+ can give stronger red emissions than the orange one due to its aragonite structure. Such emission has been explained by the Judd-Ofelt theory. It is expected that these well-defined LaBO3 assemblies could find applications in future luminescent displays and lamps.

Glucose oxidase (GOx) can react with intracellular glucose and oxygen (O2 ) to produce hydrogen peroxide (H2 O2 ) and gluconic acid, which can cut off the nutrition source of cancer cells and consequently inhibit their proliferation. Therefore, GOx is recognised as an ideal endogenous oxido-reductase for cancer starvation therapy. This process can further regulate the tumor microenvironment by increasing the hypoxia and the acidity. Thus, GOx offers new possibilities for the elaborate design of multifunctional nanocomposites for tumor therapy. However, natural GOx is expensive to prepare and purify and exhibits immunogenicity, short in vivo half-life, and systemic toxicity. Furthermore, GOx is highly prone to degrade after exposure to biological conditions. These intrinsic shortcomings will undoubtedly limit its biomedical applications. Accordingly, some nanocarriers can be used to protect GOx from the surrounding environment, thus controlling or preserving the activity. A variety of nanocarriers including hollow mesoporous silica nanoparticles, metal-organic frameworks, organic polymers, and magnetic nanoparticles are summarized for the construction of GOx-based nanocomposites for multimodal synergistic cancer therapy. In addition, current challenges and promising developments in this area are highlighted.

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).

Spherical superparticles consisting of small NaYF4:Yb, Er nanocrystals are developed with an emulsion method. Within each superparticle, many individual upconversion nanocrystals are condensed together and lots of small vacancies are simultaneously produced because of the packing of primary nanocrystals. Through the loading fluorescent dyes inside the vacancies of these superparticles during assembly, one can fine-tune the upconversion fluorescence of these superparticles. Nearly single-band red upconversion emission can also be achieved by loading suitable amounts of dyes in these superparticles.

Titania (TiO2) has been explored as a potential drug in eradicating cancer by virtue of its photocatalytic property to generate reactive oxygen species (ROS) under UV irradiation. Its clinical application, however, has been hampered by the tissue penetration depth limit of the UV light needed for its activation. The use of ‘invisible’ near-infrared (NIR) light affords greater tissue penetration depth because most tissues are ‘transparent’ to NIR light. Here, we uniformly coated TiO2 to a nanometer-sized light transducer that can upconvert highly penetrating NIR light to the activation absorption spectrum of TiO2 at UV range. Under NIR excitation, photoinduced TiO2 by the upconverted UV light results in the generation of more than one type of ROS that was stably produced under an appropriate storage condition. The amount of ROS produced was also effective in killing cancer cells in vitro, thus suggesting its potential in overcoming the current penetration depth limit.

We demonstrate a facile method to directly coat a TiO2 layer on hydrophobic NaYF4:Yb,Tm upconversion nanocrystals. Through modifying the hydrophobic nanocrystals with a surfactant layer, a conventional sol–gel route can be applied to them for TiO2 deposition. The prepared β-NaYF4:Yb,Tm@TiO2 particles show obvious photocatalytic activity under near-infrared light as well as ultraviolet light. Based on the success in preparing upconversion cores with different sizes and subsequent TiO2 coating, we have systematically investigated the effect of core sizes on their photocatalytic performance. The results suggest that upconversion fluorescence of the core and surface of the shell both have a great effect on their photocatalytic activities. A moderate core size is thus preferred, due to the competition between these two effects.

We have developed a facile method to synthesize upconversion YF3:Yb,Tm nanocrystals in ethylene glycol. These nanocrystals exhibit an assembly structure with a peanut-like appearance. A layer of TiO2 shell can be facilely coated on the YF3:Yb,Tm nanocrystals via a sol–gel process and crystallized through annealing. The developed YF3:Tb,Tm@TiO2 particles show good photocatalytic activity under the UV band and work better in the UV/NIR band of a Xe lamp, as the core particles can efficiently upconvert NIR light into UV one.

Development of MOF-based photocatalysts is intriguing research due to their structural flexibility and tremendous catalytic sites, whereas most MOFs only can take use of UV/visible light and lack of response to NIR light. Herein, we present a facile approach to integrate upconversion nanoparticles (UCNPs) with MOF to build a NIR-responsive composite photocatalyst. The MOF shell with controllable thickness can be grown on the UCNPs, thus exhibiting tunable photocatalytic activities under NIR irradiation. Furthermore, we extend visible absorption of the MOF shell by adding −NH2 groups so that the composite photocatalysts have a better utilization of UC emissions and sunlight to improve their activities. The developed composite photocatalysts have been characterized by XRD, TEM, PL, etc., and their photocatalytic performances were systematically explored. The formation and working mechanism of the composite photocatalysts were also elucidated.

The diverse biological effects of nanomaterials form the basis for their applications in biomedicine but also cause safety issues. Induction of autophagy is a cellular response after nanoparticles exposure. It may be beneficial in some circumstances, yet autophagy-mediated toxicity raises an alarming concern. Previously, it has been reported that upconversion nanoparticles (UCNs) elicit liver damage, with autophagy contributing most of this toxicity. However, the detailed mechanism is unclear. This study reveals persistent presence of enlarged autolysosomes in hepatocytes after exposure to UCNs and SiO2 nanoparticles both in vitro and in vivo. This phenomenon is due to anomaly in the autophagy termination process named autophagic lysosome reformation (ALR). Phosphatidylinositol 4-phosphate (PI(4)P) relocates onto autolysosome membrane, which is a key event of ALR. PI(4)P is then converted into phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2 ) by phosphatidylinositol-4-phosphate 5-kinase. Clathrin is subsequently recruited by PI(4,5)P2 and leads to tubule budding of ALR. Yet it is observed that PI(4)P cannot be converted in nanoparticle-treated hepatocytes cells. Exogenous supplement of PI(4,5)P2 suppresses the enlarged autolysosomes in vitro. Abolishment of these enlarged autolysosomes by autophagy inhibitor relieves the hepatotoxicity of UCNs in vivo. The results provide evidence for disrupted ALR in nanoparticle-treated hepatocytes, suggesting that the termination of nanoparticle-induced autophagy is of equal importance as the initiation.

The facet-engineered surface and interface design for photocatalytic materials has been proven as a versatile approach to enhance their photocatalytic performance. This review article encompasses some recent advances in the facet engineering that has been performed to control the surface of mono-component semiconductor systems and to design the surface and interface structures of multi-component heterostructures toward photocatalytic applications. The review begins with some key points which should receive attention in the facet engineering on photocatalytic materials. We then discuss the synthetic approaches to achieve the facet control associated with the surface and interface design. In the following section, the facet-engineered surface design on mono-component photocatalytic materials is introduced, which forms a basis for the discussion on more complex systems. Subsequently, we elucidate the facet-engineered surface and interface design of multi-component photocatalytic materials. Finally, the existing challenges and future prospects are discussed.

The induction of autophagy on exposure of cells to a variety of nanoparticles represents both a safety concern and an application niche for engineered nanomaterials. Here, we show that a short synthetic peptide, RE-1, identified by means of phage display, binds to lanthanide (LN) oxide and upconversion nanocrystals (UCN), forms a stable coating layer on the nanoparticles' surface, and effectively abrogates their autophagy-inducing activity. Furthermore, RE-1 peptide variants exhibit a differentially reduced binding capability, and correspondingly, a varied ability to reduce the autophagic response. We also show that the addition of an arginine-glycine-aspartic acid (RGD) motif to RE-1 enhances autophagy for LN UCN through the interaction with integrins. RE-1 and its variants provide a versatile tool for tuning material-cell interactions to achieve the desired level of autophagy, and may prove useful for the various diagnostic and therapeutic applications of LN-based nanomaterials and nanodevices.

Synthesis of well-defined sodium yttrium fluoride (NaYF4) nanocrystals has been achieved in nonpolar solvents, but these nanocrystals possess a hydrophobic surface and need to be surface-modified for various biological applications. Development of facile aqueous solution method to synthesize one-dimensional NaYF4 with a hydrophilic surface still remains challenging. Herein, we demonstrate a simple route to prepare hydrophilic NaYF4 nanorods by using hydrophobic NaYF4 nanospheres as precursor. It is interesting to find that hydrothermal treatment of oleic acid-capped NaYF4 nanocrystals can not only induce anisotropic growth of these nanocrystals but also change their surface properties. The hydrophilic NaYF4 nanorods synthesized in this work has been well characterized and possible formation mechanism has also been discussed.

Here we present a microemulsion route to prepare core-shell structured NaGdF4:Yb,Er@Carbon nanoparticles, in which a thin layer of hydrophilic carbon was covered on hydrophobic NaGdF4:Yb, Er nanocrystals. The prepared NaGdF4:Yb,Er@Carbon nanoparticles were uniform in a size of 25 nm, water-dispersible, and displayed good biocompatibility and strong upconversion fluorescence. Their potential for use as efficient cell-imaging probes is also demonstrated.

This manuscript describes the accurate coating of CdS nanoparticles on the surface of colloidal carbon spheres by a facile two-step, microwave-assisted method and the studies on the photocatalytic activity of the C@CdS core-shell spheres. For the coating of CdS nanoparticles, cadmium ions were incorporated into the hydrophilic shell of colloidal carbon spheres and reacted with an introduced sulfur source under a microwave field to obtain the C@CdS hybrid spheres. Using this process, the as-prepared hybrid structures preserved the good dispersity and uniformity of initial carbon spheres, and the thickness of the CdS nanoparticles shell could be varied or controlled by the irradiation time. A photoluminescence spectrum showed that the C@CdS hybrid spheres feature a broad green emission at around 494 nm (λ(ex) = 337 nm). Additionally, CdS nanospheres were successfully prepared in aqueous solution via a microwave-assisted route, and the effect of irradiation time on the products was also investigated. The studies of the photocatalytic property demonstrate that these fabricated functional hybrid structures evinced a higher photocatalytic degradation activity when exposed to visible light irradiation than that of CdS nanospheres under the same conditions.

Nanoparticles comprising of fluorescent probes and MRI contrast agents are highly desirable for biomedical applications due to their ability to be detected at different modes, optically and magnetically. However, most fluorescent probes in such nanoparticles synthesized so far are down-conversion phosphors such as organic dyes and quantum dots, which are known to display many intrinsic limitations. Here, we report a core-shell hybrid lanthanide nanoparticle consisting of an upconverting lanthanide nanocrystal core and a paramagnetic lanthanide complex shell. These nanoparticles are uniform in size, stable in water, and show both high MR relaxivities and upconversion fluorescence, which may have the potential to serve as a versatile imaging tool for smart detection or diagnosis in future biomedical engineering.

Despite plenty of reports on the preparation of Au nanorods, it remains challenging to grow uniform Au nanorods with diameters below 5 nm. In this communication, we demonstrate the facile synthesis of ultrathin Au nanorods with a uniform diameter of 2 nm and an average aspect ratio of 30. The synthesis involves the room-temperature aging of a mixture of the [AuCl(oleylamine)] complex with amorphous Fe nanoparticles in chloroform. Analysis of the growth mechanism indicates that Au nanoparticles with a high density of defects were formed at early stages, followed by etching and redeposition process that gradually led to the growth of ultrathin Au nanorods along the ⟨111⟩ direction. This growth mechanism is different from the mechanism recently reported for ultrathin Au nanowires (ref 26), where the [AuCl(oleylamine)] complex is assembled into polymer chains followed by reduction to form wires, although the template effect of oleylamine for the formation of ultrathin Au nanorods cannot be completely ruled out.

Upconverting materials, which can be efficiently excited by near infrared light and emit strong visible light through a process termed 'upconversion fluorescence', have shown great potential for use in biological labelling and imaging. Some upconverting nanoparticles such as NaYF4 doped with lanthanide ions have been synthesized; however, these nanoparticles are not soluble in water, not biocompatible and do not have functional chemical groups for conjugation of biomolecules, and as a result their bioapplications are very limited unless some surface modifications are performed. Here we report a method for one-pot synthesis of polyethylenimine/NaYF4 nanoparticles doped with lanthanide ions, which are water soluble and biocompatible. The amino groups of polyethylenimine existing on the nanoparticles can be used for attachment of biomolecules. The nanoparticles showed a spherical shape with an average size of about 50 nm. Different lanthanide ions (Yb3+, Er3+ and Tm3+) were doped into the nanoparticles, which showed strong upconversion fluorescence of different colours in aqueous solutions under excitation at 980 nm.