Dispersion Of Quantum Dots Research Articles

Colloidal Dispersions of Sterically and Electrostatically Stabilized PbS Quantum Dots: Structure Factors, Second Virial Coefficients, and Film-Forming Properties.

Electrostatically stabilized nanocrystals (NCs) and, in particular, quantum dots (QDs) hold promise for forming strongly coupled superlattices due to their compact and electronically conductive surface ligands. However, studies of the colloidal dispersion and interparticle interactions of electrostatically stabilized sub-10 nm NCs have been limited, hindering the optimization of their colloidal stability and self-assembly. In this study, we employed small-angle X-ray scattering (SAXS) experiments to investigate the interparticle interactions and arrangement of PbS QDs with thiostannate ligands (PbS-Sn2S64-) in polar solvents. The study reveals significant deviations from the ideal solution behavior in electrostatically stabilized QD dispersions. Our results demonstrate that PbS-Sn2S64- QDs exhibit long-range interactions within the solvent, in contrast to the short-range steric repulsion characteristic of PbS QDs with oleate ligands (PbS-OA). Introducing highly charged multivalent electrolytes screens electrostatic interactions between charged QDs, reducing the length scale of the repulsive interactions. Furthermore, we calculated the second virial (B2) coefficients from SAXS data, providing insights into how surface chemistry, solvent, and size influence pair potentials. Finally, we explore the influence of long-range interparticle interactions of PbS-Sn2S64- QDs on the morphology of films produced by drying or spin-coating colloidal solutions. The long-range repulsive term of PbS-Sn2S64- QDs promotes the formation of amorphous films, and screening the electrostatic repulsion by the addition of an electrolyte enables the formation of crystalline domains. These findings highlight the critical role of NC-NC interactions in tailoring the properties of functional materials made of colloidal NCs.

Breakdown cost and recycling processes of Bentonite/TiO2 quantum dots of photo and solar degradation of Congo Red dye and industrial dyes wastes

This research presents the preparation, characterization, and application of a novel bentonite- TiO2 quantum dot (Bent/TQ) nanocomposite for the efficient photodegradation of Congo Red dye, a common pollutant in industrial wastewater. The composite was prepared via a co-precipitation method followed by calcination, which facilitated the uniform dispersion of TiO2 quantum dots within the bentonite matrix. The resulting material exhibited a high specific surface area of 205.45 m2/g and an optimized band gap of 3.15 eV, making it suitable for visible light photocatalysis. The photocatalytic efficiency of Bent/TQ was evaluated under both xenon lamp irradiation and natural sunlight. The composite demonstrated a significant degradation rate constant of 23.35 × 10⁻³ s⁻1, which is comparable to that of pure TiO2 quantum dots (28.86 × 10⁻³ s⁻1). Mechanistic studies revealed that the primary active species responsible for the degradation were hydroxyl radicals (•OH), generated through the interaction of photogenerated electron-hole pairs with H2O molecules and molecular oxygen. Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD) analyses were employed to assess the mineralization efficiency of the composite. The Bent/TQ catalyst achieved a COD removal efficiency of 84.5% and a TOC reduction of 76.2% after 240 minutes of irradiation under natural sunlight. Reusability tests indicated that the photocatalyst retained approximately 80% of its original efficiency after seven consecutive cycles, though a slight decline was observed due to particle agglomeration under prolonged light exposure. The economic analysis suggested that the use of Bent/TQ nanocomposites could reduce operational costs by 29.12% compared to conventional TiO2-based systems, making it a cost-effective solution for large-scale wastewater treatment. This work highlights the potential of Bent/TQ nanocomposites as sustainable and efficient photocatalysts for environmental remediation, with future efforts aimed at enhancing their long-term stability and expanding their applicability to a broader range of pollutants.

Porous fluorine-cerium nanosheets anchored with FeOOH quantum dots for synergistic enhanced visible-light-driven photo-Fenton degradation of phenol

The utilization of two-dimensional (2D) materials to construct heterogeneous catalysts provides opportunities for environmental remediation, while the incorporation of porous structures can further enhance catalytic performance. In this work, a porous 2D FeOOH/fluorine-cerium (F-Ce) nanosheet composite was designed and synthesized by a simple impregnation-precipitation method. The unique 2D porous structure of F-Ce promoted the high dispersion of FeOOH quantum dots (QDs) (∼1.4 nm) and their tight integration to form S-scheme heterojunctions. This structure offered a greater number of active sites, and significantly improved the capacity of light absorption and the separation and migration efficiency of photogenerated carriers, thus improving catalytic activity. This catalyst achieved a phenol removal rate of 98.1 % within 20 min during the photo-Fenton reaction, which significantly surpasses pure FeOOH (32.9 %) and F-Ce (21.7 %) alone. In particular, the optimized 14FeOOH/F-Ce catalyst achieved more than 95.0 % degradation efficiency within a remarkably short period of 5 min. Mott Schottky and in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) studies demonstrated that the S-scheme charge transfer mechanism of this heterojunction synergistically enhanced the catalytic activity of the Fenton-like reaction. This study provides valuable insights for designing efficient 2D porous heterojunction catalysts for visible-light-driven Fenton applications.

Siloxane-based oligomer ligands of indium phosphide quantum dots for improving dispersion in a siloxane matrix

The ligands of indium phosphide (InP) quantum dots (QDs) were modified with siloxane-based oligomers in a two-step process to improve the dispersion of InP QDs in a siloxane-based matrix. Oleic acid ligands on InP QDs (InP-OA) were exchanged with 6-mercapto-1-hexanol. Then, the hydroxyl functional groups (–OH) of the ligands were induced to react with poly(dimethylsiloxane), diglycidyl ether terminated (PDMS-DGE) by a ring-opening reaction of epoxide. The chemical bonding between the hydroxyl groups and PDMS-DGE was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The synthesized InP QDs with PDMS-DGE ligands (InP-PDMS-DGE) were blended with acrylate-siloxane polymers to produce color conversion QD films. The photoluminescence (PL) intensity of the QD films with the InP-PDMS-DGE QDs was improved by 2.3 times compared with that of InP-OA QDs. The color conversion efficiency of the QD films was determined using a blue light-emitting diode (LED), and the QD film containing InP-PDMS-DGE QDs demonstrated a conversion efficiency of 21%, compared to a lower efficiency of 17% for a film containing InP-OA QDs. The stability of the InP-PDMS-DGE film was tested at 85°C with a relative humidity (RH) of 85%, demonstrating an improvement of 28% compared to that with an InP-OA film.

Surface Engineering Enables Efficient AgBiS2 Quantum Dot Solar Cells.

Surface ligand chemistry is vital to control the synthesis, diminish surface defects, and improve the electronic coupling of quantum dots (QDs) toward emerging applications in optoelectronic devices. Here, we successfully develop highly homogeneous and dispersed AgBiS2 QDs, focus on the control of interdot spacing, and substitute the long-chain ligands with ammonium iodide in solution. This results in improved electronic coupling of AgBiS2 QDs with excellent surface passivation, which greatly facilitates carrier transport within the QD films. Based on the stable AgBiS2 QD dispersion with the optimal ligand state, a homogeneous and densely packed QD film is prepared by a facile one-step coating process, delivering a champion power conversion efficiency of approximately 8% in the QD solar cells with outstanding shelf life stability. The proposed surface engineering strategy holds the potential to become a universal preprocessing step in the realm of high-performance QD optoelectronic devices.

Solution-Phase Synthesis and Composition-Dependent Optical Properties of Less-Toxic Multinary Ag–Mn–Sn–S Quantum Dots

Introduction Multinary quantum dots (QDs) have been promising materials as an efficient light absorber in solar light energy conversion systems. These QDs including Cu(In,Ga)(S,Se)2 and Cu2ZnSn(S,Se)4 QDs, consisting of less-toxic elements, are known for their high absorption coefficient and excellent processability. However, the cation disorder in Cu2ZnSn(S,Se)4 has been observed to cause a bandgap fluctuation and an emergence of additional antisite defects1. An effective approach to mitigating such disorder involves the substitution of Cu or Zn with larger cations. Here we focus on Ag2MnSnS4 (AMTS) due to similar optical properties with Cu2ZnSn(S,Se)4 QDs. The energy gap of bulk AMTS was reported to ca. 2.0 eV2, making it suitable for efficient solar light energy conversion systems. However, creating AMTS structures can be challenging, often requiring high temperatures or pressures. Thus, a simpler synthesis route for preparing QDs will offer a new perspective in addressing this issue, and the size reduction will enable to tune their optical bandgap. In this study, we report for the first time the solution-phase preparation of AMTS QDs. The resulting QDs exhibited composition-dependent optical properties depending on the Ag/metal ratio. Experimental The synthesis of AMTS QDs was conducted by a facile colloidal heating-up method. Precursors of corresponding metal complexes and sulfur powder were dispersed in a mixture solvent of 1-dodecanethiol (DDT) and oleylamine (OLAm), followed by the heat treatment at more than 423 K. Thus-obtained solution was subjected to centrifugation to remove large precipitates, and target QDs were isolated from the supernatant by adding methanol and ethanol as a non-solvent, followed by centrifugation. Results and Discussion AMTS QDs with diameters less than 6 nm were obtained. The absorption spectra of AMTS QDs varied with the Ag/metal ratio. The onset wavelength was blue-shifted from ca. 670 nm to ca. 500 nm with a decrease in the Ag fraction. In the case of Ag/metal= 0.50, that is, the stoichiometric Ag2MnSnS4, the bandgap was determined to 2.0 eV, being similar to the bulk bandgap of monoclinic Ag2MnSnS4 2. The optical bandgap was monotonously increased from 2.0 eV to 2.4 eV as the Ag/metal ratio decreased from 0.50 to 0.05.The electronic energy structure of AMTS QDs was determined from the ionization energy of the QDs, which was evaluated from the onset energy of the photoelectron yield spectra in air. The conduction band minimum level shifted from –3.5 eV to –3.1 eV with a decrease in the Ag fraction, while the valence band maximum was constant at ca. –5.5 eV. The crystal structure and particle morphology were almost unchanged even when the particle composition was varied, indicating that the change in bandgap resulted from the composition. The stability of QDs was improved by surface coating with a ZnS shell. Subsequent ligand exchange with a hydrophilic molecule enabled the uniform dispersion of QDs in an aqueous solution without changing their optical properties and chemical composition. These findings open up possibilities for utilizing ATMS QDs in various applications such as photocatalysis and bioimaging in aqueous media. Reference 1 J. Kumar, and S. Ingole, J. Alloys Compd., 865, 158113 (2021). 2 Frank N. Keutsch, Dan Topa, Rie Takagi Fredrickson, E. Makovicky, and W.H. Paar, Mineral. Mag. 83(2), 233–238 (2019).

Synthesis and thermophysical property characterization of aqueous graphene quantum dot dispersions for air-conditioning applications

Air-conditioning systems are on track to demand most of the electricity consumed by buildings around the world. The authors propose that dispersing quantum dots into the chilled water loops of air-conditioners represents a path towards improving the efficiency of air-conditioners. As such, the thermophysical properties of carbon-based quantum dot ‘nanofluids’ (e.g., nanoparticles dispersed in liquids) are presented in this study for sub-ambient temperatures (5–15°C)—an under-explored temperature range which requires understanding for air-conditioning applications. This study also explores dispersion stability and materials compatibility—another under-explored area in the literature which is required for commercial uptake. In this study, carbon quantum dots were synthesized via the hydrothermal route and characterized with UV–Vis, FT-IR, Raman spectroscopy, and TEM. Next, the thermophysical properties of specific heat capacity, thermal conductivity, and viscosity of the nanofluids were experimentally measured between 5 and 15°C (not previously reported for aqueous quantum dots). The highest thermal conductivity enhancement was ∼11% (compared to DI water) for 0.3 wt.% at ∼11 °C. Finally, the stability of the fluid was monitored over time and after exposing the fluids to common materials used in air-conditioning systems (e.g., copper, brass, and stainless steel). Unchanged UV–Vis spectra and the lack of sedimentation indicate that the developed dispersions are indeed suitable for chilled water air-conditioning applications.

Demonstration of quantum dot reservoir computing based on spatio-temporal optical processing

A quantum dot network, which consists of coupled structures of randomly dispersed quantum dots, has been studied as a nano-scale optical reservoir for effective machine learning processing. In this study, we defined spatio-temporal fluorescence of a quantum dot network as the reservoir output, which is due to the characteristic dynamics of the excited energy in the network induced by laser pulse irradiation. In order to verify whether a quantum dot reservoir can improve the processing efficiency of advanced machine learning applications, we performed experimental reservoir computing using a numerical model. Several parameters that were required for the construction of the model were defined from the spatio-temporal fluorescence of an experimental quantum dot reservoir. Subsequently, the corresponding reservoir computing based on the model was numerically demonstrated. Reliable performances were successfully demonstrated as sufficient error rates toward the delayed XOR task. Additionally, the dependency on quantum dot compositions of these performances was clarified.

Confined Space Dual-Type Quantum Dots for High-Rate Electrochemical Energy Storage.

Owing to the quantum size effect and high redox activity, quantum dots (QDs) play very essential roles toward electrochemical energy storage. However, it is very difficult to obtain different types and uniformly dispersed high-active QDs in a stable conductive microenvironment, because QDs prepared by traditional methods are mostly dissolved in solution or loaded on the surface of other semiconductors. Herein, dual-type semiconductor QDs (Co9S8 and CdS) are skillfully constructed within the interlayer of ultrathin-layered double hydroxides. Inparticular, the expandable interlayer provides a very suitable confined space for the growth and uniform dispersion of QDs, where Co9S8 originates from in situ transformation of cobalt atoms in laminate and CdS is generated from interlayer pre-embedding Cd2+. Meanwhile, XAFS and GGA+U calculations are employed to explore and prove the mechanism of QDs formation and energy storage characteristics as compared to surface loading QDs. Significantly, the hybrid supercapacitors achieve a high energy density of 329.2µWhcm-2, capacitance retention of 99.1%, and coulomb efficiency of 96.9% after 22000 cycles, which is superior to the reported QDs-based supercapacitors. These findings provide unique insights for designing and developing stable, ordered, and highly active QDs.

Maximization of cytochrome C oxidase enzyme activity by optimizing color conversion from red organic light-emitting diodes

Photobiomodulation (PBM) therapy using red and near-infrared (NIR) light can effectively activate cytochrome C oxidase (CCO) enzyme to promote wound healing in living organisms. To maximize this therapeutic effect, the use of a light source with a spectrum absorbed by the CCO enzyme is necessary. A red/NIR light source optimized for CCO enzyme was obtained by partially color-converting a red organic light-emitting diode with copper indium sulfide/zinc sulfide quantum dots (QDs). To increase color conversion efficiency, the dispersion of QDs was improved by using a fibrous color conversion layer (FCCL). By optimizing the QD content in the FCCL, a red/NIR light source similar to the absorption spectrum of CCO enzyme was obtained with a spectral matching ratio of 81.7 %. When this light source was used in PBM therapy, it was experimentally verified that it showed a much faster wound closure effect compared to general red light, and it was proven that this was due to increased activity of the CCO enzyme. This study is a method of obtaining a red/NIR light source for PBM suitable for a specific enzyme performing a specific function, and is particularly useful due to its excellent form factor of being large, thin, and flexible.

0D/2D Bi2MoO6 quantum dots /rGO heterojunction boosting full solar spectrum-driven photothermal catalytic CO2 reduction to solar fuels

The photothermal-catalyzed CO2 reduction is severely limited by the low carrier transport capacity. In this paper, the in-situ construction of 0D/2D Bi2MoO6 (BMO)/reduced Graphene Oxide (rGO) heterojunction was synthesized. The excellent photothermal conversion ability of rGO promotes the high dispersion of BMO quantum dots (QDs). The size of synthesized BMO QDs is about 4.26 nm and the temperature of the catalysts can quickly rise to 68.0 °C. XPS results show that the C–O–Bi interfacial electronic bridge between surface oxygen-containing groups and BMO QDs was successfully induced by modulating the degree of GO reduction. Electrons generated by BMO QDs migrate to the rGO surface rapidly, inducing rGO as a new electron-rich surface for rapid activation of CO2. The 1:5 BMO/rGO (NaBH4) CO yield reaches 186.87 μmol/g, which is 4.64 times as much as BMO QDs.

General Strategies for Preparing Hybrid Polymer/Quantum Dot Nanocomposites for Color Conversion

Quantum dots (QDs), with their exceptional optical properties, have emerged as promising candidates to replace traditional phosphors in lighting and display technologies. This study delves into the integration strategies of QDs within glass and polymer matrices to engineer advanced quantum dot color converters (QDCCs) at the industrial scale for practical applications. To achieve enhancements in the photostability and thermal stability of QDCCs, we explore two distinct approaches: the dispersion of QDs in a hydrophilic glass matrix via a sol–gel process and the incorporation of QDs into a non-polar acrylate monomer to formulate QD/polymer nanocomposites. This research further investigates the optical behaviors of these composites, focusing on their light-scattering and propagation mechanisms, which are critical for optimizing light extraction efficiency in QDCCs. Additional optical film and light-scattering particles can improve color conversion efficiency by ~140%. These advancements present a significant step forward in the development of high-performance, energy-efficient, QD-based lighting and display systems.

One-Dimensionally Arranged Quantum-Dot Superstructures Guided by a Supramolecular Polymer Template.

Colloidal quantum dots (QDs) exhibit important photophysical properties, such as long-range energy diffusion, miniband formation, and collective photoluminescence, when aggregated into well-defined superstructures, such as three-dimensional (3D) and two-dimensional (2D) superlattices. However, the construction of one-dimensional (1D) QD superstructures, which have a simpler arrangement, is challenging; therefore, the photophysical properties of 1D-arranged QDs have not been studied previously. Herein, we report a versatile strategy to obtain 1D-arranged QDs using a supramolecular polymer (SP) template. The SP is composed of self-assembling cholesterol derivatives containing two amide groups for hydrogen bonding and a carboxyl group as an adhesion moiety on the QDs. Upon mixing the SP and dispersed QDs in low-polarity solvents, the QDs self-adhered to the SP and self-arranged into 1D superstructures through van der Waals interactions between the surface organic ligands of the QDs, as confirmed by transmission electron microscopy. Furthermore, we revealed efficient photoinduced fluorescence resonance energy transfer between the 1D-arranged QDs by an in-depth analysis of the emission spectra and decay curves.

One‐Dimensionally Arranged Quantum‐Dot Superstructures Guided by a Supramolecular Polymer Template

AbstractColloidal quantum dots (QDs) exhibit important photophysical properties, such as long‐range energy diffusion, miniband formation, and collective photoluminescence, when aggregated into well‐defined superstructures, such as three‐dimensional (3D) and two‐dimensional (2D) superlattices. However, the construction of one‐dimensional (1D) QD superstructures, which have a simpler arrangement, is challenging; therefore, the photophysical properties of 1D‐arranged QDs have not been studied previously. Herein, we report a versatile strategy to obtain 1D‐arranged QDs using a supramolecular polymer (SP) template. The SP is composed of self‐assembling cholesterol derivatives containing two amide groups for hydrogen bonding and a carboxyl group as an adhesion moiety on the QDs. Upon mixing the SP and dispersed QDs in low‐polarity solvents, the QDs self‐adhered to the SP and self‐arranged into 1D superstructures through van der Waals interactions between the surface organic ligands of the QDs, as confirmed by transmission electron microscopy. Furthermore, we revealed efficient photoinduced fluorescence resonance energy transfer between the 1D‐arranged QDs by an in‐depth analysis of the emission spectra and decay curves.

Stability of binary colloidal mixtures of Au noble metal and ZnS semiconductor nanoparticles

Controlling the stability of colloidal nanoparticles in multicomponent systems, i.e., mixtures of colloids, is of vital importance for product formulations and separation processes of nanoparticles. However, very few studies are currently found in literature regarding the generation of binary colloids by mixing of colloidal nanoparticles, particularly small nanoparticles (< 20 nm). In this study, we report on the development of a stable binary colloid made of nanoparticles of different sizes and compositions. As a model system for this study, we mixed aqueous dispersions of gold nanoparticles (Au NPs) and ZnS quantum dots (QDs). We investigated the stability of Au NPs with three different surface ligands after mixing them with ZnS QDs, both before and after functionalization of the Au NPs with bis(p-sulfonatophenyl) phenylphosphine (BSPP). We used UV–visible spectroscopy as the primary method to monitor stability of nanoparticles in the binary mixture over time. We found out that the released thioglycerol and acetate from the surface of ZnS QDs to the binary mixture induces agglomeration in Au NPs. The surface chemistry and the purification process of Au NPs after their synthesis and surface treatment were identified as key parameters to regulate the stability in the mixture. Thus, we successfully achieved a stable mixture of BSPP-functionalized Au NPs with ZnS QDs as a model of a stable binary mixture. We believe that this study is important to stimulate research directed towards real-world multicomponent formulations including their characterization and the understanding of surface interactions.

Determination of carbon nanoparticle dispersion solubility parameters using the classic Hansen and the DiPEVa method

Hansen's three-dimensional Solubility Parameter (3DSP) are widely recognized for assessing the compatibility of a dispersed phase with a continuous phase. A modified approach, known as the DiPEVa method, has recently emerged in the literature. This method refines 3DSP by incorporating surface tension considerations. Given the presence of these two similar methodologies, the objective of this study is to conduct a comparative analysis between the two approaches, employing carbon nanoparticles, including graphene oxide, carbon quantum dots (produced via microwave pyrolysis of Spirulina microalgae, and the reaction between citric acid and ethylenediamine), graphene nanoplatelets, and carbon nanotubes as the focal subjects. To achieve this, assessing solubility parameters involved dispersing these nanoparticles in 32 organic solvents with well-established solubility parameters. Subsequently, the collected data underwent a genetic algorithm optimization, facilitating the computation of the Hansen 3D dispersibility sphere. This process included the calculation of the 3DSP for the sphere's central point and its interaction radius (R0). Quality-of-fit metrics, such as DataFit values and the percentage of outliers, were computed to assess the accuracy of the models. As a result, it was evident that the DiPEVa method outperformed the Hansen method in most cases, except for carbon quantum dot dispersion obtained through Spirulina pyrolysis, where both methods yielded comparable results.

Simultaneous inclusion of quantum dots in multi-functional layers of thin film organic solar cells

The role of quantum dot (QD) decoration in the hole transport buffer layer and the photoactive medium on the photovoltaic parameters of thin film organic solar cells (TFOSCs) was investigated. A cadmium–tellurium-based QD was synthesized successfully and embedded in two of the functional layers of a TFOSC to improve its overall power conversion efficiency. The experimentally determined optimum concentration of the QD was maintained in the interfacial layer to investigate the effect of QD concentration in the active layer. The observed increased short-circuit current density (Jsc) and open circuit voltage (Voc) are attributable to the enhanced energy level tuning, broadened optical absorption, and charge transport process facilitated by the integration of QDs inside the media. Moreover, an improved device efficiency was obtained when the solvent additive was introduced into the bulk heterojunction photoactive layer films to facilitate QD dispersion and increase the interpenetrating network of the active layer blend that reduces the occurrence of trap sites, which, in turn, limits the Auger recombination rates. The QD-doped TFOSCs catalyzed with solvent additives displayed an enhanced overall photovoltaic parameter, which is quite appreciable in comparison with that of the pristine devices.

Employing carbon quantum dots to combat cytomegalovirus

Carbon quantum dots (CQDs) are well known as a promising therapeutic agent due to their excellent pro-oxidant, antioxidant, antibacterial and anticancer properties under visible light irradiation. This material is easy to produce by several bottom-up or top-down methods. In this study, we used citric acid as starting precursor to synthesize aqueous carbon quantum dots dispersion by pyrolysis at 210 °C. Atomic force microscopy and XPS analyses revealed that CQDs synthesized are quasi-spherical with typical diameter of 9 nm and lots of C–O and CO functional groups distributed over the basal plane and edges of the dots. Here, we investigated the antiviral properties of CQDs against cytomegalovirus (CMV). The pre-treatment with CQDs upregulates interferon-stimulated genes (ISG), resulting in better virus control. Cellular defence against cytomegalovirus of CQDs pre-treated cells is increased in a dose-dependent manner. Our results reveal high biocompatibility and potent in vitro antiviral properties of CQDs.

Facile synthesis of ZnCdS quantum dots via a novel photoetching MOF strategy for boosting photocatalytic hydrogen evolution

MOF self-sulfurizing is regarded as a promising approach for preparing quantum dots (QDs). Herein, ZnCdS QDs were constructed by photoetching self-sulfurization of a novel 3D metal–organic framework (namely PZH) for the first time. The results of the morphology and X-ray diffraction (XRD) characterizations show that the ZnCdS QDs do not self-aggregate, and the frame structure of PZH remain intact. Under visible-light irradiation, ZnCdS QDs/PZH with the photoetching time of 60 min (ZnCdS−3/PZH) exhibits a remarkably enhanced photocatalytic hydrogen production rate with an apparent quantum efficiency (AQE) of 18.51 % at 420 nm. The improvement of photocatalytic activity can be predominantly attributed to an outstanding four synergism of promoting separation and transfer of carriers owing to ZnCdS QDs shortening the charge transmission distance, inhibiting the recombination of photogenerated electron-holes of uniform dispersed quantum dots without aggregating, optimizing the adsorption behavior of the active intermediates (H*) owing to the synergistic action between ZnCdS QDs and PZH, offering more holes for reactant molecules transmission due to presence of PZH. The density functional theory (DFT) calculation reveals that ZnCdS quantum dots relative to large size S-ZnCdS is going to help reduce the Gibbs free energy of photocatalytic hydrogen evolution reaction. More importantly, this rare strategy not only flourish the design idea of quantum dots, but also promote the applications of MOF in photocatalytic H2 production.

Synthesis of TiO2 nanotubes from ilmenite with CuS nanoparticles as efficient visible-light photocatalyst.

Titanium dioxide nanotube (TNT) is one of the most widely used photocatalysts. In this research, TNT was prepared by a facile method using ilmenite (FeTiO3) concentrate as the titanium source. For this purpose, iron was leached out from ilmenite using HCl in assistance with the iron powder as the reducing agent to produce pure TiO2, where consequently, TNT was produced through hydrothermal treatment of the prepared TiO2 in an alkaline solution. CuS quantum dots, using the L-cysteine as a linker, were coated on the TNT to improve TNTs' photocatalytic properties. Characterization was done using XRD, SEM, FESEM, HRTEM, FT-IR, nitrogen sorption, and band gap measurement. The results revealed the formation of TNT with a star-shaped macrostructure as well as, a good dispersion of uniform CuS quantum dots with an average diameter of a few nanometers on the TiO2 structure. A dye adsorption kinetics study of the TNT and CuS-dopped TNT showed that TNT carries a higher adsorption capacity compared to the CuS-dopped TNT, developed due to its higher surface area and pore volume. Next, the photocatalytic performance (under visible light) of the prepared composite was studied over the methylene blue (MB) and malachite green (MG) dyes, after the determination of the dye adsorption equilibrium point (where the adsorption stops). TNT showed almost no dye degradation while the prepared composite degraded almost 95 % of the dyes as the result of the reduced band gap from 3.21 to 2.67 eV. In this study, for the first time, the TNT was prepared using a mineral source and ilmenite, enhanced in photocatalytic properties, and presented a successful application.