Single ZnO Research Articles

Hexagonal ZnO microdisk grown by mist chemical vapor deposition on c-plane sapphire substrate and lasing actions

Abstract Hexagonal ZnO microdisks were grown by mist chemical vapor deposition (mist-CVD) for 6 h. The microdisks when viewed from the top were typically hexagonal with diameters of a few micrometers, and their typical three-dimensional shape was a hexagonal pyramid. Sharp peaks appeared in the room-temperature photoluminescence (PL) spectra observed from a single hexagonal ZnO microdisk under high optically pumped conditions, and they are assumed to correspond to lasing actions. We also examined the temperature dependence of these sharp peaks in the PL spectra.


Microbial biosurfactant-mediated green synthesis of zinc oxide nanoparticles (ZnO NPs) and exploring their role in enhancing chickpea and rice seed germination

Malnutrition is one of the greatest challenges faced by humanity, which may be addressed by improving crop productivity to ensure food security. However, extensive use of synthetic fertilizers can lead to soil fertility degradation. This study highlights the potential of combining nanotechnology with biotechnology to enhance the germination rates of commercially important crop seeds. Bacterial biosurfactant extracted from a newly isolated Klebsiella sp. strain RGUDBI03 was used as a reducing and capping agent for the synthesis of zinc oxide nanoparticles (ZnO NPs) through a simple method. Extensive characterization of ZnO NPs through electron microscopic analysis showed well-dispersed, homogeneous NPs with a size range of 2–10 nm. High-resolution transmission electron microscopy (HR-TEM) images also revealed molecular fringes of 0.26 nm in single crystal ZnO NPs, with approximately 50% of the NPs exhibiting a size range of 2–4 nm. X-ray diffraction (XRD) results of ZnO NPs indicated the presence of (100), (002), (101), (102), (200), and (112) planes, confirming their crystalline nature. The presence of C = C–H, C = C, C–H, and C = C groups in both the bacterial biosurfactant and ZnO NPs, as depicted by Fourier-transform infrared spectroscopy (FTIR) spectra, confirmed the function of the biosurfactant as a reducing and capping agent. The nano-primed chickpea (Cicer arietinum) and rice (Oryza sativa) seeds showed an increase in water uptake rate, 89% and 92% respectively, compared to the control (73% and 44%), leading to an enhanced germination rate of 98% and 76%, compared to their respective controls (80% and 30%) under optimized conditions. Additionally, the nano-primed seeds exhibited higher levels of α-amylase activity in both seeds (0.37 mg/g for chickpea and 2.49 mg/g for rice) compared to the control. Notably, the ZnO NP priming solution exhibited no cytotoxicity on red blood cells and earthworms (Eudrilus eugeniae), indicating their non-cytotoxic and eco-friendly nature for future field trials.

Спектральный отклик единичной нанопроволоки ZnO

Miniaturization of devices based on one-dimensional semiconductor nanocrystals is of high importance for high-frequency applications, photonics, and various sensors. Zinc oxide, one of the materials actively studied for such purposes, can be obtained by several technologies. Among them, chemical vapor deposition is distinguished by a low concentration of defects in the resulting structures. The aim of this work was to fabricate a test device on a single ZnO nanocrystal by means of nanomanipulation and to study its spectral response in the range from near-IR to UV. Since one of the promising applications of ZnO is UV sensors, the task was to test the selectivity of the response to the wavelength range below 400 nm.

Single walled carbon nanotubes/ZnO nanowires heterostructure array for NO2 gas sensing at low ppm levels

A layer-by-layer ZnO nanowire (NW)-Single Walled Carbon Nanotube (CNT) hybrid gas sensor has been proposed for effective detection of NO2 gas under a low exposure limit of 5 ppm. The fabricated hybrid sensor displayed good sensor response (S %), good selectivity and fast response time towards the target gas. S % value of 36.4 % under 5 ppm NO2 level at 250 °C and good selectivity response towards different interfering gases like SO2, CO and H2 have been observed. Meanwhile, fast response time values of 44.08 s (response) and 62.11 s (recovery) were observed at 300 °C under 5 ppm NO2 level. The sensor baseline resistance of the hybrid heterostructure (HS) was also found to be lower when compared to that of a bare ZnO NW sensor. In addition, the presence of Single Walled CNT in the HS was also shown to reduce the operational temperature of the sensor. Temperature played a significant role by controlling the adsorption and desorption kinetics of gas molecules on the surface. Moreover, the formation of p-n interface between Single Walled CNT (p-type) and ZnO NW (n-type) might have modulated the potential charge barrier on interacting with the adsorbed gases which inturn might have impacted the response of the hybrid sensor. In addition, the large surface areas offered by both NWs and nanotubes might have improved the gas adsorption capability thereby enhancing the overall hybrid sensor’s response.

Single ZnO Nanowire for Electrical and Optical NO2 Gas Sensing: Origin of Reversible and Irreversible Gas Effects Investigated by Photoluminescence Spectroscopy.

In this work, the gas sensing properties of a single ZnO nanowire (NW) are investigated, simultaneously in terms of photoluminescence (PL) and photocurrent (PC) response to NO2 gas, with the purpose of giving new insights on the gas sensing mechanism of a single 1D ZnO nanostructure. A single ZnO NW sensing device was fabricated, characterized, and compared with a sample made of bundles of ZnO NWs. UV near-band-edge PL emission spectroscopy was carried out at room temperature and by lowering the temperature down to 77 K, which allows detection of resolved PL peaks related to different excitonic transition regions. Surface effects were observed in PL maps, considering different nano and microstructures. Electrical and optical measurements were acquired at the same time during the NO2 gas exposure, allowing for the comparison of PL and PC response times and signal recovery. During NO2 gas desorption, irreversible behavior in the surface-related and donor-acceptor pair (DAP) regions is interpreted as the effect of an initial transient when electronic transfer from the gas molecules to the bulk occurs through the ZnO NW surface which acts as a channel. To the best of our knowledge, this is the first work which investigates the simultaneous PL optical and PC electrical response signals of a single ZnO NW to gas exposure.

Improvement of photocatalytic hydrogen production performance of ZnO with Bi2X3 (X = Te, Se)

ABSTRACT Harnessing photocatalysts to facilitate the visible-light-driven breakdown of water molecules is esteemed as a highly auspicious and ecologically sustainable approach for hydrogen production. This study aimed to improve the hydrogen production performance of single ZnO photocatalysts by preparing efficient Bi2Te3/ZnO and Bi2Se3/ZnO composite photocatalysts by microwave method. During the synthesis process, both Bi2Te3 and Bi2Se3 were fully fused and reacted with ZnO to form heterojunctions using magnetic stirring and microwave heating. The experimental results indicate a significant enhancement in the hydrogen production activity of the BT-Z and BS-Z composite photocatalysts. When the Bi2Te3 content is 5%, with a microwave temperature maintained at 135 °C and a microwave time of 90 min, the hydrogen production rate reaches 664.286 μmol∙h−1∙g−1 within 4 hr. On the other hand, when the Bi2Se3 content is 5%, with a microwave temperature maintained at 135 °C and a microwave time of 90 min, the hydrogen production rate reaches 515.306 μmol∙h−1∙g−1 within 4 hr.

Antibacterial Properties and Application of Bi2Sn2O7/ZnO Composite Photocatalytic Materials.

In this experiment, Bi2Sn2O7/ZnO composite photocatalytic materials were synthesized by a hydrothermal method and characterized by XRD, SEM, and EDS, etc. The prepared Bi2Sn2O7/ZnO has a nanorod structure and high phase purity. The photocatalytic antimicrobial performance of Bi2Sn2O7/ZnO against bacteria and fungi under visible light was significantly better than that of single Bi2Sn2O7 and ZnO. In particular, 1000 mg/L 1 : 3 Bi2Sn2O7/ZnO showed an antimicrobial rate of more than 97 % against Escherichia coli, Staphylococcus aureus, and Candida albicans, which are widely present in the nature. The free radical trapping experiments were selected and the antimicrobial mechanism was investigated, and the results showed that the antimicrobial process of the Bi2Sn2O7/ZnO system was regulated by the free radicals such as ⋅OH, h+, and e-, which were generated by its unique photocatalytic activity. Finally, MTT cytotoxicity experiments demonstrated that the Bi₂Sn₂O₇/ZnO composite was not toxic to cells. In addition, the antimicrobial performance of Bi2Sn2O7/ZnO on real livestock wastewater and the real-life application of the prepared Bi2Sn2O7/ZnO PCL composite antibiotic film for antimicrobial treatment of freshly cut fruits' surfaces under visible light were experimentally investigated. This study provides a new idea for Bi2Sn2O7/ZnO as a photocatalytic antimicrobial agent.

A photo rechargeable capacitor based on the p–n heterojunction of ZnO/ZIF-67 showing enhanced photovoltage

The photo rechargeable device (PRD) has been continuously drawing attention because it combines energy conversion and storage in one device. As for the photoelectrode of PRD, the construction of heterojunction is of crucial importance to enhance the photo performance. In this work, a two-electrode photo rechargeable capacitor based on the p–n heterojunction of ZnO/ZIF-67 is fabricated. ZIF-67 not only serves as the energy storage material but also forms the p–n heterojunction together with ZnO. A fast volatilization method was adopted for the in situ growth of ZIF-67 on ZnO nanorods to ensure sufficient mass loading and fewer interface defects. The results show a photovoltage of 0.36 V (0.2 V higher than single ZnO), a specific capacitance of 759.0 mF/g, and an overall energy conversion efficiency of 0.49%. The enhanced photovoltage is attributed to the p–n heterojunction. Moreover, a practical button cell was also fabricated, with 91% Coulombic efficiency remaining after 3000 cycles in the dark.

Mixture toxicity study of two metal oxide nanoparticles and chlorpyrifos on Eisenia andrei earthworms.

Co-exposure soil studies of pollutants are necessary for an appropriate ecological risk assessment. Here, we examined the effects of two-component mixtures of metal oxide nanoparticles (ZnO NPs or goethite NPs) with the insecticide chlorpyrifos (CPF) under laboratory conditions in short-term artificial soil assays using Eisenia andrei earthworms. We characterized NPs and their mixtures by scanning electron microscopy, atomic force microscopy,dynamic light scattering and zeta potential, and evaluated effects on metal accumulation, oxidative stress enzymes, and neurotoxicity related biomarkers in single and combined toxicity assays. Exposure to ZnO NPs increased Zn levels compared to control in single and combined exposure (ZnO NPs + CPF) at 72h and 7days, respectively. In contrast, there was no indication of Fe increase in organisms exposed to goethite NPs. One of the most notable effects on oxidative stress biomarkers was produced by single exposure to goethite NPs, showing that the worms were more sensitive to goethite NPs than to ZnO NPs. Acetylcholinesterase and carboxylesterase activities indicated that ZnO NPs alone were not neurotoxic to earthworms, but similar degrees of inhibition were observed after single CPF and ZnO NPs + CPF exposure. Differences between single and combined exposure were found for catalase and superoxide dismutase (goethite NPs) and for glutathione S-transferase (ZnO NPs) activities, mostly at 72h. These findings suggest a necessity to evaluate mixtures of NPs with co-existing contaminants in soil, and that the nature of metal oxide NPs and exposure time are relevant factors to be considered when assessing combined toxicity, as it may have an impact on ecotoxicological risk assessment.

Nano‐engineering in zinc‐based catalysts for CO2 electroreduction: Advances and challenges

AbstractElectrocatalytic CO2 reduction (CO2RR), an emerging sustainable energy technology to convert atmospheric CO2 into value‐added chemicals, has received extensive attention. However, the high thermodynamic stability of CO2 and the competitive hydrogen evolution reaction lead to poor catalytic performances, hardly meeting industrial application demands. Due to abundant reserves and favorable CO selectivity, zinc (Zn)‐based catalysts have been considered one of the most prospective catalysts for CO2‐to‐CO conversion. A series of advanced zinc‐based electrocatalysts, including Zn nanosheets, Zn single atoms, defective ZnO, and metallic Zn alloys, have been widely reported for CO2RR. Despite significant progress, a comprehensive and fundamental summary is still lacking. Herein, this review provides a thorough discussion of effective modulation strategies such as morphology design, doping, defect, heterointerface, alloying, facet, and single‐atom, emphasizing how these methods can influence the electronic structure and adsorption properties of intermediates, as well as the catalytic activity of Zn‐based materials. Moreover, the challenges and opportunities of Zn‐based catalysts for CO2RR are also discussed. This review is expected to promote the broader application of efficient Zn‐based catalysts in electrocatalytic CO2RR, thus contributing to a future of sustainable energy.

Simple two-step synthesis of Ag/ZnO nanoparticles with enhanced photocatalytic response

This study presents a simple two-step synthesis method for the fabrication of Ag/ZnO nanocomposites to improve the photocatalytic response of ZnO. The synthesis involves ZnO nanoparticles that were fabricated from the thermal decomposition of commercial zinc acetate. In order to produce Ag/ZnO nanoparticles in a simple two-step process, ZnO nanoparticles were mixed with Ag nanoparticle suspensions previously obtained by the laser ablation of solids in liquids technique at three different fluences. Structural characterization of ZnO powders revealed the presence of single phase wurtzite ZnO nanoparticles with crystal sizes of 20 nm. On the other hand, XRD patterns for a composite sample revealed the presence of signals associated to both ZnO and Ag suggesting that silver nanoparticles were attached to the ZnO particles surface. Optical characterization of the ZnO powders, carried out by UV–vis spectroscopy, showed a strong absorption band centered at 380 nm, which is associated to excitonic transitions in ZnO nanoparticles, whilst absorption measurements of silver nanoparticles colloids revealed the presence of a strong band centered near 412 nm. This band shifts to shorter wavelengths with increasing fluence from 2.6 to 6.2 J cm−2, indicating changes in nanoparticles size. Photocatalytic degradation tests of methylene blue under UV irradiation were carried out using pure ZnO, Ag colloids and Ag/ZnO nanoparticles. After the first 30 min of irradiation, it was observed that the silver nanoparticles reached degradation percentages of 16, 22 and 29% for samples synthesized at 2.6, 4.2 and 6.2 J cm−2, respectively. Meanwhile the ZnO sample reached a value of 13% after 30 min. Regarding the Ag/ZnO composite sample, the percentage of degradation after 30 min was 36%, demonstrating a considerable enhanced photocatalytic activity as compared to ZnO. After 24 h irradiation, Ag/ZnO degraded 95% of the methylene blue solution. It was observed that decorating ZnO with laser produced silver nanoparticles accelerates the photocatalytic response of ZnO by enhancing the activity at short times.

Construction of Z-scheme ZnO/g-C3N4 photocatalytic systems for degradation of dyeing wastewater

A novel heterogeneous nanocomposite photocatalyst ZnO/g-C3N4 was fabricated by secondary high-temperature calcination using g-C3N4 and ZnO as raw materials and characterized by XRD, SEM, TEM, EDS, FT-IR, Zeta potential, UV-Vis and XPS. The results displayed that the ZnO/g-C3N4 components were tightly bound, evenly distributed and significantly reduced in size, which could provide more active sites. The heterogeneous types, photocatalytic performance, degradation mechanism of ZnO/g-C3N4 for dyeing wastewater were speculated by REDOX potential, heterojunction, and quenching experiments. The degradation efficiency of ZnO/g-C3N4 on MB was much higher compared with that of single ZnO, g-C3N4 and the mechanical mixture of ZnO and g-C3N4, which can reach more than 95% at 60 min. The degradation rate was also significantly improved, with the degradation rate exceeding 50% at 20 min. The composite ZnO/g-C3N4 could degraded 90% MB after 5 cycles. The quenching experiment showed that hydroxyl (·OH) and photogenerated hole (h+) played the main role in the reaction process. It was confirmed that the prepared ZnO/g-C3N4 formed a Z-scheme photocatalytic system by examining the transfer paths of e- and h+ in various types of heterojunction and contrasting the CB and VB energy levels with the REDOX potentials of ZnO and g-C3N4. The Z-Scheme ZnO/g-C3N4 photocatalyst has the characteristics of stability, reusability, and no by-product, making it an ideal choice for environmental purification.

Highly responsive and swift recovery triethylamine gas sensor based on NiCo2O4-ZnO p-n heterojunction

In the detection of food freshness and chemical production, live tracking of the concentration of triethylamine gas is both essential and challenging. The NiCo2O4-ZnO triethylamine gas sensor prepared with two-step hydrothermal method proposed in this study exhibits a response of TEA at the ideal operational temperature of 250 °C and a response/recovery time of 69 s/2 s. Compared to the single ZnO sensor, the response value is increased by a factor of 8.47, the recovery time is reduced to 1/8, and good selectivity (the response for TEA is 4.75 times higher than others), repeatability, and long-term stability (40 days) are demonstrated. Notably, research on fabricating TEA gas sensors by constructing p-n heterojunctions using NiCo2O4 and ZnO composites is currently lacking. The enhancement of the gas-sensitive properties of the composites is the result of a combination of factors such as increased specific surface area (18.18 m2/g−1) and pore size (29.84 nm), the formation of p-n heterojunctions, and the synergistic effect between the two materials. The excellent TEA sensitivity exhibited by the NiCo2O4-ZnO composites holds considerable practical application potential in triethylamine gas sensors.

High-performance, low-power, and flexible ultraviolet photodetector based on crossed ZnO microwires p-n homojunction

Low-power, flexible, and integrated photodetectors have attracted increasing attention due to their potential applications of photosensing, astronomy, communications, wearable electronics, etc. Herein, the samples of ZnO microwires having p-type (Sb-doped ZnO, ZnO:Sb) and n-type (Ga-doped ZnO, ZnO:Ga) conduction properties were synthesized individually. Sequentially, a p-n homojunction vertical structure photodiode involving a single ZnO:Sb microwire crossed with a ZnO:Ga microwire, which can detect ultraviolet light signals, was constructed. When exposed under 360 nm light illumination at −0.1 V, the proposed photodiode reveals pronounced photodetection features, including a largest on/off ratio of 105, responsivity of 2.3 A/W, specific detectivity of ∼6.5×1013 Jones, noise equivalent power of 4.8×10−15 W Hz−1/2, and superior photoelectron conversion efficiency of ∼7.8%. The photodiode also exhibits a fast response/recovery time of 0.48 ms/9.41 ms. Further, we propose a facile and scalable construction scheme to integrate a p-ZnO:Sb⊗n-ZnO:Ga microwires homojunction component into a flexible, array-type detector, which manifests significant flexibility and electrical stability with insignificant degradation. Moreover, the as-constructed array unit can be integrated into a practical photoimaging system, which demonstrates remarkable high-resolution single-pixel imaging capability. The results represented in this work may supply a workable approach for developing low-dimensional ZnO-based homojunction optoelectronic devices with low-consumption, flexible, and integrated characteristics.

Influence of ZnSb2O6 Doping on Phase, Electrical and Dielectric Properties of ZnO Varistors

AbstractThe present investigation reports the variations of the microstructure and electrical properties due to a change in the ZnSb2O6 content of ZnO varistors. The impact of the ZnSb2O6 additive on both microstructure and electrical properties in ZnO varistors is studied via the X‐ray diffraction (XRD) and an impedance analyzer. Zn7Sb2O12 spinel phase and single hexagonal ZnO phase are detected in ZnO varistors with the addition of ZnSb2O6. The ZnO varistors with 5 mol% ZnSb2O6 have the highest nonlinear coefficient (43.2) and the lowest leakage current density (3.96 A cm−2). The resistivity of grain boundary ρgb increases continuously with the increasing content of ZnSb2O6 as demonstrated by impedance measurements. Additionally, low values of dielectric loss at high frequencies suggest a ZnO varistor doped with ZnSb2O6 is suitable for high frequency device applications.

Integrating interface engineering and plasmonic effect to boost photoresponse performance of ZnO:Ga/GaN heterojunction self-powered UV photodetectors

The ability to function without an external power supply makes photodetectors highly promising for use in a new generation of wirelessly and independently operated ultraviolet (UV) photodetection and imaging systems. However, self-powered photodetectors' high dark current, inadequate light harvesting, and poor carrier separation prevent them from attaining high-efficiency UV photodetection and imaging. Herein, a high-performance heterojunction UV photodetector consisting of a single Ga-doped ZnO microwire enshrouded by Ag nanowires (AgNWs@ZnO:Ga MW), a MgO electron blocking layer, and a p-type GaN wafer was proposed. Taking full advantage of the interface engineering and plasmonic effects, the AgNWs@ZnO:Ga MW/MgO/GaN photodetector achieves high photodetection performance with an excellent responsivity of 262 mA/W, a remarkable external quantum efficiency of 92.37%, and a high detectivity of 1.966 × 1012 Jones under 370 nm illumination with power density of 0.22 mW/cm2. Furthermore, it also demonstrates ultrafast pulsed photoresponse speed with a rise/fall time of 3.64 μs/252 μs. An UV imaging system is designed based on the AgNWs@ZnO:Ga MW/MgO/GaN self-powered photodetector, allowing for high-quality, accurate, and distinct object imaging. This work combines interface engineering and plasmonic effects for achieving high-performance UV photodetection, which provides a strategic approach to the development of highly efficient optoelectronic devices.

Light and voltage dual-modulated volatile resistive switching in single ZnO nanowires.

A single ZnO nanowire device with volatile resistive switching behavior has been prepared. Different from traditional resistive switching devices, such ZnO nanowire devices do not exhibit resistive switching behaviors under a single bias voltage, and appear resistive switching behavior under the combined action of light stimuli and bias voltage. Through the demonstration of the time-dependent hysteresis curve and atmosphere-dependent hysteresis loop of the resistive switching devices, it is believed that under the resistive switching process, ultraviolet illumination can increase the carrier concentration and modulate the barrier depletion structure, and external bias voltage can ionize the surface state. They work together to modulate the switching process of the devices. Such light stimuli and bias voltage dual-modulated resistive switching device enables optical control and may thus be considered for sensory applications or optically tunable memories.

Epitaxial ZnO piezoelectric layer on SiO2/Mo solidly mounted resonator fabricated using epitaxial Au sacrificial layer

In solidly mounted resonator (SMR) type of bulk acoustic wave resonator, it is difficult to fabricate single crystalline piezoelectric thin films in a bottom-up process due to the amorphous SiO2 in the low acoustic impedance layer of the acoustic Bragg reflector. In this study, single crystalline ZnO piezoelectric layer on amorphous SiO2/polycrystalline Mo acoustic Bragg reflector is fabricated using a wet etching process of the epitaxial Au sacrificial layer. Epitaxial growth of ZnO was confirmed by X-ray diffraction pole figure and transmission electron microscope electron diffraction pattern. Resonance frequency of 1.3 GHz of epitaxial ZnO SMR was observed using a network analyzer.

Fabricating AC/DC nanogenerators based on single ZnO nanowires by using a nanomanipulator in a scanning electron microscope

Single zinc oxide nanowires (ZnO NWs) are promising for nanogenerators because of their excellent semiconducting and piezoelectric properties, but characterizing the latter efficiently is challenging. As reported here, an electrical breakdown strategy was used to construct single ZnO NWs with a specific length. With the high operability of a nanomanipulator in a scanning electron microscope, ZnO-NW-based two-probe and three-probe structures were constructed for fabricating AC/DC nanogenerators, respectively. For a ZnO NW, an AC output of between −15.31 mV and 5.82 mV was achieved, while for a DC nanogenerator, an output of ∼24.3 mV was realized. Also, the three-probe structure’s output method was changed to verify the distribution of piezoelectric charges when a single ZnO NW is bent by a probe, and DC outputs of different amplitudes were achieved. This study provides a low-cost, highly convenient, and operational method for studying the AC/DC output characteristics of single NWs, which is beneficial for the further development of nanogenerators.

Core-shell ZnO@TiO2 hexagonal prism heterogeneous structures as photoanodes for boosting the efficiency of quantum dot sensitized solar cells.

In quantum dot sensitized solar cells (QDSSCs), the photoanode provides a stable support for the quantum dots, and promotes the production of photogenerated electrons and the transfer to external circuit. Therefore, it is very important to search for excellent photoanodes for the commercial application of QDSSCs. In this paper, a core-shell ZnO@TiO2 hexagonal prism heterogeneous structure was prepared by a two-step hydrothermal method. The ZnO@TiO2 heterogeneous structure not only has a unique 1D hexagonal prism morphology, but also can effectively inhibit the electron-hole recombination and has a greater light response and higher collection efficiency while speeding up the electron transmission rate. By adjusting the concentration of the TiO2 source, the best photoanode material Zn@Ti-2 was explored, and it showed excellent cell performance: Jsc = 25.4 mA cm-2, Voc = 0.71 V, PCE = 8.5%, and FF = 0.49. Compared with a single ZnO photoanode, the PCE value is increased by 25%. EIS, Tafel polarization and transient photocurrent responses confirm that the Zn@Ti-2 photoanode has higher catalytic activity and stability. Therefore, Zn@Ti-2 may be a promising photoanode material for QDSSCs.