Reduced Charge Recombination Research Articles

Kinetic study of the enhanced photoelectrochemical properties of microwave-assisted Al and Si co-doped Zr-Fe2O3 photoanodes

Unintended metal oxide layer development during co-doping has been suggested as being highly effective in intensifying the oxygen evolution reaction. Herein, we studied the influence of microwave-assisted co-doping of trivalent Al3+ and tetravalent Si4+ into Zr-Fe2O3 photoanode for effective photoelectrochemical (PEC) performance. The Si co-doping showed effective diffusion into the hematite bulk during high-temperature quenching. Relative to SiOx, an Al2O3 layer notably passivated the surface defects, whilst Si4+ co-doping markedly improved the bulk charge transfer features, compared to Al3+ co-doping. Because of the active passivation effect of the Al2O3 layer, the photocurrent density of Al/Zr-Fe2O3 photoanode was considerably increased at lower potentials. In specific, the Al/Zr-Fe2O3 photoanode displayed an almost 100% enhancement in surface charge transfer rate constant than that of the bare Zr-Fe2O3 at 1.23 VRHE. The comprehensive experimental results provided evidence of the consequence of tri/tetravalent co-dopants on charge transfer in the bulk of the hematite and at the photoanode-electrolyte interface. A probable charge transfer mechanism was proposed under illumination to demonstrate how the Si and Al microwave-assisted attachment impacted the photogenerated charge recombination reduction in the photoanode and subsequently advanced its PEC water splitting performance.

Schottky-junction plasmonic nanocomposite: A non-hazardous excellent visible light photocatalyst for industrial waste management

A bio-compatible nanocomposite “Ag/Ag doped TiO2” with UV–Visible-NIR light gathering quality was synthesized by solvothermal method, followed by green synthesis method. Insertion of Ag+ ions into Ti2+ lattice sites in Ag doped TiO2 alters the n-type TiO2 semiconductor to p-type. Nanostructured doped TiO2 suffers high charge recombination loss in presence of trapped states, resulting 35 % photocatalytic efficiency. Ag decoration on p-type Ag doped TiO2 forms a Schottky barrier at metal-semiconductor junction, which reduces charge recombination loss by separating the photogenerated electron-hole (e-h) in two materials of the nanocomposite. These photogenerated charges create oxide and hydroxide super radicals in the aqueous system of photocatalyst, ensuing 80% degradation of SO dye under 50 min white light illumination. The nanocomposite also demonstrated good performance in degradation of industrial dyes like 50% Mordant Orange (MO) and 15% Direct Blue (DB) under 50 min white light irradiation. DFT analysis of the heterosystems supports absorptivity tuning of experimentally obtained nanocomposite. Moreover, the nanocomposite proved its non-toxicity to human cells, as it reveals <20% cell death with maximum dose (250 µg/ml) of the nanocomposite in cytotoxicity test. Hence, proper designing and synthesizing the nanocomposite explored an eco-friendly solar photocatalyst for industrial waste management.

Synergistic Effect of Size-Tailored Structural Engineering and Postinterface Modification for Highly Efficient and Stable Dye-Sensitized Solar Cells.

Despite significant progress in device performance, dye-sensitized solar cells (DSSCs) continue to fall short of their theoretical potential. Moreover, research in recent years needs to pay more attention to improving the device fabrication process. To achieve the theoretical efficiency limit, it is crucial to optimize the interface between the dye and TiO2 nanoparticles in the entire device stack. Our study indicates that optimizing the structure or size of the coadsorbents and implementing a monolayer adsorption process can be an effective strategy to reduce charge recombination and enhance light-harvesting properties. Our research aims to develop a surface-coating adsorbent plan that controls the TiO2 nanoparticle interface to achieve the radiative limit of power conversion efficiency (PCE). Specifically, we utilized 2-thiophenecarboxylic acid (THCA) or chenodeoxycholic acid (CDCA) as postinterfacial surface-coating adsorbents. Our results demonstrate that this approach effectively achieves the desired PCE limit. Combined with the coadsorbent structure engineering and interface optimization, the device increased the packing area on the TiO2 nanoparticles' surface, reaching an improved PCE of over 13.17% under simulated sunlight (1.5G), which is the highest efficiency of a porphyrin single dye-based DSSC. In particular, this practical approach was also applied to a large-area DSSC with an area of 3 cm2, yielding a remarkable PCE of 9.04%. Furthermore, when applied to a polymer gel electrolyte, this novel approach recorded the highest PCE of 11.16% with a long-term operational stability of up to 1000 h for the quasi-solid-state DSSCs. Our research findings provide a promising avenue for achieving high-performance DSSCs with ease of access and demonstrate practical applications as alternatives to conventional power sources.

Additive engineering by tetrabutylammonium iodide for antimony selenosulfide solar cells

Antimony selenosulfide (Sb2(S,Se)3) solar cells have attracted great attention due to their tunable optoelectronic properties, ease of preparation and low toxicity. However, the harmful intrinsic defect density and internal nonradiative recombination of Sb2(S,Se)3 hinder its practical usage. In this work, a facile additive approach is explored to modify the Sb2(S,Se)3 solar cell efficiency by using tetrabutylammonium iodide (TBAI). After applying a certain amount of TBAI into the Sb2(S,Se)3 precursor solution, the film surface presents lower cracks and roughness than that of the pristine sample. It also increases its hydrophobicity and n-type nature revealed by contact angle and work function measurements. Moreover, the incorporation of TBAI during the formation of the Sb2(S,Se)3 layer improves the quality of the film effectively suppresses its defect trap density, which manifests as a reduction in charge recombination and enhancement of the power conversion efficiency (PCE) when incorporated into solar cells. The fabricated device with 0.62 mol% of TBAI shows the highest PCE (8.87%) and high stability without encapsulation, maintaining about 91% of its initial efficiency after 60 d in air. The results provide a feasible strategy to the ongoing progress of reliable Sb2(S,Se)3 devices.

Construction of novel an in-situ m-BiVO4/t-BiVO4 isotype heterojunction photocatalyst for improved visible light-dependent degradation of dye

In this article, we have studied the photocatalytic characteristics of isotype heterostructure Bismuth vanadate BiVO4 (m-BiVO4/t-BiVO4). The isotype Bismuth vanadate m-BiVO4/t-BiVO4 (MTBV) was formed by a facile hydrothermal method. It was observed that the crystalline phase of isotype MTBV could be controlled by modifying the pH values of the precursors in the hydrothermal method. The isotype MTBV heterojunction was investigated for its physicochemical features by different techniques including X-ray powder diffraction (XRPD), Field emission scanning electron microscopy (FESEM), Energy dispersive microscopy (EDS), Fourier transfer infrared (FTIR) spectroscopy, UV–visible diffuse reflectance spectroscopy (UV–Vis DRS), Photoluminance (PL), and Electrochemical impedance spectroscopy (EIS). Photocatalytic degradation of Congo red (CR) dye under visible light irradiation was used to determine the photocatalytic activity of a well-developed MTBV heterostructure. The isotype MTBV phase resulted in an increased response due to a faster electron-hole pair formation rate by reducing charge recombination processes, a reduction in optical energy band gap (2.52 eV), and good compatibility between Preston t-BiVO4 and m-BiVO4 photocatalyst. In 1 hr, the optimized isotype MTBV heterojunction showed a CR degradation of 98%. According to the results of the PL, EIS, and UV–Vis studies, isotype MTBV might be an excellent option for a blue/green visible light-dependent optical photocatalyst. A feasible photocatalytic mechanism was suggested and discussed in particular to relate the physiochemical properties and photocatalytic properties; furthermore, kinetics decomposition process study, scavenger effect, dye concentration, catalyst dose effect, reusability and stability were checked, respectively.

Surface Engineering of Cu2O Photocathodes via Facile Graphene Oxide Decoration for Improved Photoelectrochemical Water Splitting.

Copper oxide (Cu2O) has attracted significant interest as an efficient photocathode for photoelectrochemical (PEC) water splitting owing to its abundance, suitable band gap, and band-edge potential. Nevertheless, a high charge recombination rate restricts its practical photoconversion efficiency and reduces the PEC water-splitting performance. To address this challenge, we present the facile electrodeposition of graphene oxide (GO) on the Cu2O photocathode surface. To determine the effect of varying GO weight percentages on PEC performance, varying amounts of GO were deposited on the Cu2O photocathode surface. The optimally deposited GO-Cu2O photocathode exhibited a photocurrent density of -0.39 to -1.20 mA/cm2, which was three times that of a photocathode composed of pristine Cu2O. The surface decoration of Cu2O with GO reduced charge recombination and improved the PEC water-splitting performance. These composites can be utilized in strategies designed to address the challenges associated with low-efficiency Cu2O photocathodes. The physicochemical properties of the prepared samples were comprehensively characterized by field-emission scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Raman spectroscopy, UV-visible spectroscopy, and X-ray photoelectron spectroscopy. We believe that this research will pave the way for developing efficient Cu2O-based photocathodes for PEC water splitting.

Managing Excess Lead Iodide with Functionalized Oxo‐Graphene Nanosheets for Stable Perovskite Solar Cells

AbstractStability issues could prevent lead halide perovskite solar cells (PSCs) from commercialization despite it having a comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long‐term stability is gaining incremental importance. Excess lead iodide (PbI2) causes perovskite degradation, although it aids in crystal growth and defect passivation. Herein, we synthesized functionalized oxo‐graphene nanosheets (Dec‐oxoG NSs) to effectively manage the excess PbI2. Dec‐oxoG NSs provide anchoring sites to bind the excess PbI2 and passivate perovskite grain boundaries, thereby reducing charge recombination loss and significantly boosting the extraction of free electrons. The inclusion of Dec‐oxoG NSs leads to a PCE of 23.7 % in inverted (p‐i‐n) PSCs. The devices retain 93.8 % of their initial efficiency after 1,000 hours of tracking at maximum power points under continuous one‐sun illumination and exhibit high stability under thermal and ambient conditions.

Managing Excess Lead Iodide with Functionalized Oxo-graphene Nanosheets for Stable Perovskite Solar Cells.

Stability issues could refrain from commercializing lead halide perovskite solar cells (PSCs) despite having comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long-term stability is gaining incremental importance. Excess lead iodide (PbI2) causes perovskite degradation, although it aids in crystal growth and defect passivation. Herein, we synthesized functionalized oxo-graphene nanosheets (Dec-oxoG NSs) to effectively manage the excess PbI2. Dec-oxoG NSs provide anchoring sites to bind the excess PbI2 and passivate perovskite grain boundaries, thereby reducing charge recombination loss and significantly boosting the extraction of free electrons. The inclusion of Dec-oxoG NSs leads to a PCE of 23.7% in inverted (p-i-n) PSCs. Devices retain 93.8% of their initial efficiency after 1,000 hours of tracking at maximum power points under continuous one-sun illumination, and exhibit high stability under thermal and ambient conditions.

Revolutionizing the Role of Solar Light Responsive BiVO4/BiOBr Heterojunction Photocatalyst for the Photocatalytic Deterioration of Tetracycline and Photoelectrocatalytic Water Splitting.

In this study, a series of BiVO4/BiOBr composites with varying mole ratios were successfully synthesized using a hydrothermal method. The in-situ synthesis strategy facilitated the formation of a close interfacial contact between BiVO4 and BiOBr at the depletion zone, resulting in improved charge segregation, migration, reduced charge recombination, enhanced solar light absorption capacity, promoting narrow band gap, and large surface area. This study investigates the influence of different mole ratios of BiVO4 and BiOBr in a BiVO4/BiOBr nanocomposite on the photocatalytic degradation of tetracycline (TC), a pharmaceutical pollutant, and photoelectrocatalytic water splitting (PEC) under solar light irradiation. Maximum decomposition efficiency of ~90.4% (with a rate constant of 0.0159 min-1) for TC was achieved with 0.5 g/L of 3:1 BiVO4: BiOBr (31BVBI) photocatalyst within 140 min. The degraded compounds resulting from the TC abatement were analyzed using GC-MS. Furthermore, TC standards exhibited 78.2% and 87.7% removal of chemical oxygen demand (COD) and total organic carbon (TOC), respectively, while TC tablets showed 64.6% COD removal and 73.8% TOC removal. The PEC water splitting experiments demonstrated that the 31BVBI photoanode achieved the highest photocurrent density of approximately 0.2198 mA/cm2 at 1.23 V vs. RHE, resulting in the generation of approximately 1.864 mmolcm-2 s-1 of hydrogen, while remaining stable for 21,600 s. The stability of the photocatalyst was confirmed by post-degradation characterizations, which revealed intact crystalline planes, shape, and surface area. Comparisons with existing physicochemical methods used in industries indicate that the reported photocatalyst possesses strong surface catalytic properties and has the potential for application in industrial wastewater treatment and hydrogen generation, offering an advantageous alternative to costly and time-consuming processes.

MOF-derived spinel NiMn2O4/CoMn2O4 heterojunction and its application in a high-performance photocatalyst and supercapacitor

Metal oxide heterojunctions have attracted considerable attention in photocatalyst and supercapacitor applications. In this study, NiMn2O4/CoMn2O4 (NMO/CMO) heterojunctions were synthesized using ternary metal-organic frameworks (MOFs) as precursors. After calcination at 500 °C, the as-prepared NMO/CMO composite maintains the porous sheet-like morphology of the ternary MOF, exhibiting a highly porous structure. The heterostructured NMO/CMO composite demonstrates enhanced photocatalytic performance compared with pure NMO and CMO. This enhancement may be attributed to the well-aligned energy levels at the NMO/CMO interface, which effectively reduces charge recombination and facilitates the efficient transport of photogenerated carriers. In addition, the NMO/CMO heterojunction exhibits enhanced supercapacitor performance owing to the increased number of active redox sites and reduced charge transfer resistance. When tested at 3 A/g, the NMO/CMO composite displays a higher capacitance (756.4 F/g) than pure NMO (579.6 F/g) and CMO (519.6 F/g) and remarkable rate capability, maintaining a capacitance of 639 F/g even at 10 A/g. Notably, asymmetric supercapacitors fabricated using NMO/CMO and activated carbon can achieve an energy density of 32.18 W h/kg at 750 W/kg and superior cycling life, retaining 92.1% of its initial capacitance after 3000 cycles.

Improved Photovoltaic Performances of Lead‐Free Cs2AgBiBr6 Double Perovskite Solar Cells Incorporating Tetracene as Co‐Hole Transport Layer

Cs2AgBiBr6 double perovskite compounds are increasingly studied in recent years as promising candidates able to counter polluting, harmful, and oxygen‐/moisture‐sensitive issues intrinsic to traditional lead‐containing solar cells. Exhibiting high optical absorption coefficient, low toxicity, and important structural stability, Cs2AgBiBr6 solar cells still suffer from limited absorption of low‐energy photons, low carrier mobility, and limited carrier lifetimes induced by defect states. Herein, for the first time, a molecular layer of tetracene is introduced within a Cs2AgBiBr6‐based photovoltaic architecture: being incorporated at the interface between the double perovskite photoabsorber and spiro‐OMeTAD hole transport material, tetracene allows for a suitably graded cascade of energy bands within the solar cell architecture, which ultimately improves interfacial charge transfers and reduces charge recombination. The performances in photovoltaic devices are consequently enhanced versus tetracene‐free configurations, with champion values of open‐circuit voltages of 1.1 V (vs. 1.0 V), current densities of 2.5 mA cm−2 (vs. 1.9 mA cm−2), and photoconversion efficiencies of 1.7% (vs. 1.3%) with reduced hysteretic behavior.

Promising SnOx electron transport layer for polymer solar cells

In this study, SnOx films were synthesized via thermal oxidation of Sn films at various temperatures ranging from 300 °C to 500 °C. The impact of oxidation temperature on the structural, optical, and electronic properties of the SnOx films was investigated using SEM, EDX, optical absorption, and impedance spectroscopy techniques. It was found that the oxidation temperature has a significant impact on the SnOx resistance, which decreases as the temperature increases due to improved SnOx crystallinity and enhanced electron mobility. Furthermore, an increase in recombination resistance suggests an improvement in interface quality and reduced charge recombination processes. Finally, the impact of SnOx electron transport layer properties on the photovoltaic characteristics of organic solar cells was investigated. It was observed that OSCs based on SnOx ETL obtained at higher oxidation temperature reveal enhanced photovoltaic characteristics.

BaSnO3-SnO2 heterojunction mesoporous photoanode for quantum dot-sensitized solar cells

Mesoporous photoanodes, as quantum dot adsorption framework and electron transfer paths, are the key components in efficient quantum dot-sensitized solar cells (QDSSCs). Binary heterojunction mesoporous photoanodes hold promise for facilitating electron transport due to the heterojunction potential, when compared to conventional mono-component mesoporous photoanodes. In this work, we construct a binary mesoporous photoanode with enhanced mesoporous and electron transport using a BaSnO3-SnO2 heterojunction, and then fabricated CdSe/CdS co-sensitized QDSSCs. The charge extraction, open-circuit voltage decay, electrochemical impedance spectroscopy, and intensity-modulated voltage/photocurrent spectroscopy measurements demonstrated that, in contrast to the BaSnO3 mesoporous photoanode, the BaSnO3-SnO2 mesoporous photoanode could effectively reduce charge recombination and extend the electron lifetime, thus promoting charge collection in the QDSSCs. Based on these merits, the BaSnO3-SnO2 mesoporous photoanode-based solar cells yielded a power conversion efficiency of 3.14%, resulting in a ca. 11% increase in power conversion efficiency, compared to the reference BaSnO3 solar cells.

Influence of metal salts (Al, Ca, and Mg) on the work function and hole extraction at carbon counter electrodes in perovskite solar cells

Hole transport material-free carbon-based perovskite solar cells (HTM-free C–PSCs) are recognized as a cost-effective and stable alternative to conventional perovskite solar cells. However, the significant energy level misalignment between the perovskite layer and the carbon counter electrode (CE) results in ineffective hole extraction and unfavorable charge recombination, which decreases the power conversion efficiency (PCE). Here, we report the introduction of metal salts (Al, Ca, and Mg) into graphite/carbon black (Gr/CB) CEs to modify the work function and enhance the hole selectivity of the CE. This modification leads to improved energy level alignment, efficient hole extraction, and reduced charge recombination. The PCE of the HTM-free C-PSC based on Al-modified Gr/CB as the CE material reached 9.91%, which is approximately 12% higher than that of devices employing unmodified Gr/CB CEs. This work demonstrates that by directly incorporating metal salts into the Gr/CB CE, the energy level alignment and hole extraction at the perovskite/carbon interface can be improved. This presents a viable method for enhancing the PCE of HTM-free C–PSCs.

C60-CN: A bifunctional interface modification material for perovskite solar cells

Titanium dioxide (TiO2) is regularly used as an electron transport material in n-i-p perovskite solar cells (PSCs). However, massive defects exist on the TiO2 surface, which will lead to serious hysteresis and interface charge recombination of the device, thus affecting the device’s efficiency. In this study, a cyano fullerene pyrrolidine derivative (C60-CN) was synthesized and applied to PSCs for the first time to modify the TiO2 electron transport layer. Systematic studies have shown that the addition of the C60-CN modification layer on the TiO2 surface will enlargement the perovskite grain size, improve the perovskite film quality, enhance electron transport, and reduce charge recombination. The C60-CN layer can significantly reduce the density of trap states in the perovskite solar cells. As a result, the PSCs based on C60-CN/TiO2 obtained a power conversion efficiency (PCE) of 18.60%, suppressing the hysteresis and improving the stability, whereas the PCE of the control device using the original TiO2 ETL was lower, 17.19%.

Nitrogen-Doped Graphene Quantum Dot–Tin Dioxide Nanocomposite Ultrathin Films as Efficient Electron Transport Layers for Planar Perovskite Solar Cells

Tin dioxide (SnO2) has recently been recognized as an excellent electron transport layer (ETL) for perovskite solar cells (PSCs) due to its advantageous properties, such as its high electron mobility, suitable energy band alignment, simple low-temperature process, and good chemical stability. In this work, nitrogen-doped graphene quantum dots (N-GQDs) were prepared using a hydrothermal method and then used to fabricate N-GQD:SnO2 nanocomposite ultrathin films. N-GQD:SnO2 nanocomposite ultrathin films were investigated and applied as electron transport layers in planar PSCs. The presence of N-GQDs with an average size of 6.2 nm in the nanocomposite improved its morphology and reduced surface defects. The excitation–emission contour map indicated that the N-GQDs exhibited a remarkably enhanced light-harvesting capability due to the possibility of absorbing UV light and producing emissions in the visible range. The quenching of photoluminescence spectra showed that the N-GQDs in nanocomposite ultrathin films improved electron extraction and reduced charge recombination. As a result, the power conversion efficiency (PCE) of our planar PSCs fabricated with the optimized N-GQD:SnO2 nanocomposite electron transport layer was improved by 20.4% over pristine SnO2-based devices.

Unfused-ring acceptor based on a quinoxaline unit functionalized with meta-positioned alkoxy chains for efficient organic solar cells with high open-circuit voltage

Owing to the simple synthesis and flexible chemical modifiability of unfused-ring non-fullerene acceptors (UF-NFAs), they have gained great research attraction for fabricating organic solar cells (OSCs). However, UF-NFA-based devices still underperform fused-ring non-fullerene acceptor-based devices. Herein, a series of UF-NFAs based on a fluorinated quinoxaline (Qx) building block functionalized with meta-positioned alkoxy chains, namely FQxOC8-H, FQxOC8-F, and FQxOC8-Cl, are synthesized. Density-functional theory (DFT) calculations demonstrated that all UF-NFAs exhibited good backbone coplanarity, owing to the S⋯N and H⋯F nonbonding interactions. The resulting UF-NFAs showed broad absorption ranged from 500 to 900 nm as well as deep highest occupied molecular orbital (HOMO) levels. FQxOC8-Cl exhibited more red-shifted and greater absorption coefficient owing to the stronger molecular stacking caused by chlorine atoms of the end groups. Moreover, PM6:FQxOC8-Cl-based blended film exhibited reduced charge recombination, higher carrier mobilities, and suitable phase-separation domains. Accordingly, OSCs based on FQxOC8-Cl yielded a superior power conversion efficiency (PCE) of 10.52%. In contrast, FQxOC8-H-based device afforded a lower efficiency of 6.13%. Our work indicates that combining the fluorinated Qx motif functionalized with meta-positioned alkoxy chains with electron-withdrawing end-groups showed great potential to construct efficient UF-NFAs.

Enhanced sub-1 eV detection in organic photodetectors through tuning polymer energetics and microstructure.

One of the key challenges facing organic photodiodes (OPDs) is increasing the detection into the infrared region. Organic semiconductor polymers provide a platform for tuning the bandgap and optoelectronic response to go beyond the traditional 1000-nanometer benchmark. In this work, we present a near-infrared (NIR) polymer with absorption up to 1500 nanometers. The polymer-based OPD delivers a high specific detectivity D* of 1.03 × 1010 Jones (-2 volts) at 1200 nanometers and a dark current Jd of just 2.3 × 10-6 ampere per square centimeter at -2 volts.We demonstrate a strong improvement of all OPD metrics in the NIR region compared to previously reported NIR OPD due to the enhanced crystallinity and optimized energy alignment, which leads to reduced charge recombination. The high D* value in the 1100-to-1300-nanometer region is particularly promising for biosensing applications. We demonstrate the OPD as a pulse oximeter under NIR illumination, delivering heart rate and blood oxygen saturation readings in real time without signal amplification.

P, K doped crystalline g-C3N4 grafted with cyano groups for efficient visible-light-driven H2O2 evolution

Graphitic carbon nitride (g-C3N4), especially in heptazine forms, has long been considered as a promising non-toxic, benign and sustainable photocatalyst for producing the important chemical and potential green energy H2O2. However, bulk g-C3N4 shows moderate activity originated from its intrinsic drawbacks such as restricted visible-light harvesting ability and sluggish charge separation. Herein, a co-modified crystalline g-C3N4 by P, K ions and cyano group was successfully synthesized via co-thermal polymerization of precursors followed by molten salt treatment. The advanced g-C3N4 exhibits an outstanding photocatalytic H2O2 generation yield of 4424 μmol g−1h−1, more than 81-fold of the pristine counterpart, also superior than that of g-C3N4 processed by single modification treatment. This superior photocatalytic H2O2 evolution efficiency is attributed to the rational design of crystalline g-C3N4, enabling super visible photons capture, more efficient charge carries separation and substantially reduced charge recombination. The current work may furnish an integratable strategy for solar fuel production.

A Composite of TiO2 Quantum Dots and TiO2 Nanoparticles Coated on Anti-Bumping Glass Beads (TiO2QDs-TiO2NPs/GBs), with a Very Low Content of TiO2 as a High Performance Photocatalyst

A composite of TiO2 quantum dots (TiO2QDs) and TiO2 nanoparticles (TiO2NPs) was successfully deposited on glass beads (GBs), with a very low content of TiO2 (&lt;0.3 wt%), by a rapid, simple, inexpensive, and scalable synthesis method. The TiO2QDs-TiO2NPs/GBs catalyst possesses an extremely high photocatalytic performance under simulated solar irradiation, with the complete degradation of the aqueous solutions of methylene blue in 60 minutes of photodegradation. There were no changes in the catalytic activity after six times of recycling. The superior performance of the catalyst should be attributed to the role of the synergistic effect between TiO2NPs and TiO2QDs to prevent the accumulation of TiO2 nanoparticles during the oxidation reaction, to improve the absorption in the visible region, to enhance the immigration of photogenerated electrons and holes in interfaces of two materials in the TiO2QDs-TiO2NPs composite, which leads to a reduced charge recombination rate, and to generate midgap states and suppress the recombination of electron-hole pairs.