Design and Synthesis of NTU-9/C3N4 Photocatalysts: Effects of NTU-9 Content and Composite Preparation Method.

Hybrid materials based on graphitic carbon nitride (g-C3N4) and NTU-9 metal-organic frameworks (MOF) were designed and prepared via solvothermal synthesis and calcination in air. The as-prepared photocatalysts were subsequently characterized using Brunauer-Emmett-Teller (BET) analysis, UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) emission spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The obtained NTU-9/C3N4 composites showed a greatly improved photocatalytic performance for the degradation of toluene in the gas phase under LED visible-light irradiation (λmax = 415 nm). The physicochemical properties and photocatalytic activities of the obtained NTU-9/C3N4 materials were tuned by varying the NTU-9 content (5-15 wt%) and preparation method of the composite materials. For composites prepared by calcination, the photocatalytic activity increased with decreasing NTU-9 content as a result of the formation of TiO2 from the MOFs. The best photocatalytic performance (65% of toluene was photodegraded after 60 min) was achieved by the NTU-9/C3N4 sample prepared via the solvothermal method and containing 15 wt% MOF, which can be attributed to the appropriate amount and stable combination of composite components, efficient charge separation, and enhanced visible-light absorption ability. The photocatalytic mechanisms of the prepared hybrid materials depending on the preparation method are also discussed.

Synergy between AgInS2 quantum dots and ZnO nanopyramids for photocatalytic hydrogen evolution and phenol degradation.

Despite the unique properties of single semiconductor nanomaterials and quantum dots, poor photocatalytic activity has characterized them and the fabrication of nanocomposites has become necessary to enhance their photocatalytic performance. Thus, AgInS2 quantum dots (AIS QDs, 4.0 ± 1.6 nm), have been successfully prepared and loaded onto ZnO nanopyramids (ZnO NPy). The effect of the nominal amount of AIS QDs decorating ZnO NPy on the morphology, optical properties, structure and surface chemistry of the nanocomposites was systematically studied. Photocatalytic tests revealed that the 1%AIS@ZnO NPy sample reported the highest photoactivity for phenol degradation in aqueous phase (92 % after one hour of irradiation, λ > 350 nm) that was 4 and 68 times the reported for bare ZnO NPy and AIS QDs, respectively. Accordingly, the maximum photocatalytic hydrogen evolution, under UV-vis light, for the same sample corresponded to 17 and 21 times the estimated for pristine ZnO NPy and AIS QDs, respectively. Hence, the AIS QDs - ZnO system has been applied in the photocatalytic field for the first time in this work and a synergetic effect was confirmed owing to a strong heterojunction formation between both semiconductors that allows an enhanced charge carrier separation, improving the photocatalytic activity.

Preparation of CdS and Bi2S3 quantum dots co-decorated perovskite-type KNbO3 ternary heterostructure with improved visible light photocatalytic activity and stability for phenol degradation.

CdS quantum dot-decorated KNbO3 composite photocatalysts co-modified with Bi2S3 QDs were designed and synthesized by a combination of the hydrothermal method with a linker-assisted adsorption route, using starch and thioglycolic acid as capping agents, which facilitated the attachment of modifiers to the surface of potassium niobate. The quantum dots were successfully deposited onto the surface of the perovskite-type KNbO3 with a good dispersion and a stable heterostructure was formed. The as-prepared photocatalysts were subsequently characterized by UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) specific surface area, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) emission spectroscopy. The obtained KNbO3-based composites showed greatly improved photocatalytic performance for the degradation of phenol in the aqueous phase under visible light irradiation (λ > 420 nm) over pristine KNbO3. The highest photocatalytic performance and enhanced stability were observed for the ternary 30% CdS-5%Bi2S3 quantum dot-decorated KNbO3 composite, which could be related to the enhanced visible-light absorption ability, efficient charge separation in the three-level electron transfer heterojunction, improved stability and appropriate amounts of composite components. The formation of a surface layer of CdO decreased the visible light photoactivity of the CdS QD-decorated KNbO3 photocatalysts. The main phenol oxidation intermediates were benzoquinone, catechol, hydroquinone, and 1,2,4-benzenetriol, which underwent further photooxidation to form non-cyclic organic acids. Action spectral analysis proved the better photocatalytic activity of the ternary CdS/B2S3 QDs co-decorated KNbO3 composite compared to the binary CdS QDs decorated KNbO3 sample and revealed that irradiation ranging from 420 to 520 nm was responsible for the visible light photoactivity.

Design, Synthesis, and Enzymatic Evaluation of Novel ZnO Quantum Dot-Based Assay for Detection of Proteinase 3 Activity.

Herein, the synthesis and application of functionalized quantum dot-based protease probes is described. Such probes are composed of nontoxic ZnO nanocrystals decorated by amino groups followed by linker and labeled peptide attachment. Spherical NH2-terminated ZnO quantum dots (QDs) with the average size ranging from 4 to 8 nm and strong emission centered at 530 nm were prepared using the sol-gel method. The fluorescence of ZnO QDs was quenched by the BHQ1 moiety present on the N-terminal amino group of the peptide. The enzymatic cleavage of the peptide mediated by the proteinase 3 (PR3) bond resulted in an increase in the QD probe fluorescence. This observation was verified using both model and biological systems; and the picomolar detection limit was found to be more than 30 times lower than that of the previously reported internally quenched peptide (a decrease in detection limit from 43 to 1.3 pmol was observed).

Quantum dot-decorated semiconductor micro- and nanoparticles: A review of their synthesis, characterization and application in photocatalysis.

Quantum dot (QD)-decorated semiconductor micro- and nanoparticles are a new class of functional nanomaterials that have attracted considerable interest for their unique structural, optical and electronic properties that result from the large surface-to-volume ratio and the quantum confinement effect. In addition, because of QDs' excellent light-harvesting capacity, unique photoinduced electron transfer, and up-conversion behaviour, semiconductor nanoparticles decorated with quantum dots have been used widely in photocatalytic applications for the degradation of organic pollutants in both the gas and aqueous phases. This review is a comprehensive overview of the recent progress in synthesis methods for quantum dots and quantum dot-decorated semiconductor composites with an emphasis on their composition, morphology and optical behaviour. Furthermore, various approaches used for the preparation of QD-based composites are discussed in detail with respect to visible and UV light-induced photoactivity. Finally, an outlook on future development is proposed with the goal of overcoming challenges and stimulating further research into this promising field.

Surface properties and photocatalytic activity of KTaO3, CdS, MoS2 semiconductors and their binary and ternary semiconductor composites.

Single semiconductors such as KTaO3, CdS MoS2 or their precursor solutions were combined to form novel binary and ternary semiconductor nanocomposites by the calcination or by the hydro/solvothermal mixed solutions methods, respectively. The aim of this work was to study the influence of preparation method as well as type and amount of the composite components on the surface properties and photocatalytic activity of the new semiconducting photoactive materials. We presented different binary and ternary combinations of the above semiconductors for phenol and toluene photocatalytic degradation and characterized by X-ray powder diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area and porosity. The results showed that loading MoS2 onto CdS as well as loading CdS onto KTaO3 significantly enhanced absorption properties as compared with single semiconductors. The highest photocatalytic activity in phenol degradation reaction under both UV-Vis and visible light irradiation and very good stability in toluene removal was observed for ternary hybrid obtained by calcination of KTaO3, CdS, MoS2 powders at the 10:5:1 molar ratio. Enhanced photoactivity could be related to the two-photon excitation in KTaO3-CdS-MoS2 composite under UV-Vis and/or to additional presence of CdMoO4 working as co-catalyst.