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ZnO films with well-aligned hierarchical structures have been successfully synthesized at moderate temperatures using a simple catalyst-free hydrothermal process. The synthesized ZnO films are found to be single-phase, with a hexagonal wurtzite-type structure. Scanning electron microscopy images show that the well-aligned hierarchical structures are assembled with interlaced parallel sheets grown on the (400) silica surface. The water contact angle measurement indicates that the water on the films has a contact angle of about 156.3°. This clearly demonstrates that the ZnO films synthesized by this simple method have superhydrophobic properties and may be important for applications in self-cleaning surfaces, biology, and so on.

Studies on photocatalytic degradation of lignin are scarce, even though it is an effective method for treatment of industrial effluents. In the present work, an advanced oxidation process (AOPs), leading to the photodegradation of lignin aqueous solutions, is proposed by using microstructured (T-MT) and nanostructured (T-NT) titanium dioxide compounds. Hydrothermal synthesis, in accordance with an experimental factorial design considering time of synthesis, NaOH concentration and synthesis temperature, was used to produce tunable TiO₂ photocatalysts for further study of its effects on the degradation of lignin. Photocatalytic reactions were conducted in a micro reactor batch system under UV irradiation. The catalysts were analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area and porosity analyzer (BET), energy-dispersive X-ray spectroscopy (EDS) and UV-Vis diffuse reflectance spectroscopy. In order to optimize the yield reaction, an experimental factorial design was performed. According to our results, nanostructured TiO₂ consisting in different structural features and light absorption properties were produced using this method. It is shown that T-MT and T-NT compounds exhibit a wide range of values, for the kinetic parameters, in photoinduced degradation of methylene blue (MB) and lignin.

A one-step facile method of synthesizing fluorescent carbon dots (CDs) has been demonstrated, whereby fluorescent CDs are produced through hydrothermal treatment of glucose in the presence of H₃BO₃ with a fluorescence quantum yield of 14.5%. It is found that spherical CDs have an average size of 3.7nm as well as good monodispersion in aqueous solution. The added Cr (VI) selectively leads to the inner filter effect (IFE)-based fluorescence quenching of the CDs. Such fluorescence responses can be used for well quantifying Cr (VI) in the range of 0.05–200$\mu$M. Significantly, the CDs possess negligible cytotoxicity, excellent biocompatibility and high selectivity. All these features are favorable for label-free monitoring of Cr (VI) in complex biological samples. It was then successfully applied for the fluorescence imaging of intracellular Cr (VI). As an efficient chemosensor, the CDs hold great promise in broadening their applications in biological systems.

In this work, reduced graphene oxide/CeO₂ nanocomposites (RGO/CeO₂) with two different RGO contents were synthesized using a facile one-step hydrothermal method, and the microwave absorption properties of RGO/CeO₂ were investigated for the first time. Morphology and structure analysis shows that the CeO₂ nanoparticles are uniformly dispersed on the RGO sheets with average size of 15nm. The as-prepared RGO/CeO₂ exhibits excellent microwave absorbability. An optimal reflection loss (RL) of $-$32dB is found at 17GHz with a coating layer thickness of 1.5mm. The product with a coating layer thickness of only 2.0mm shows a bandwidth of 4.3GHz, corresponding to RL at $-$10dB (90% of electromagnetic wave absorption). Compared with pristine RGO or pure CeO₂ nanoparticles, the reported nanocomposites achieved both wider and stronger wave absorption in the frequency range of 2–18GHz. The enhanced microwave absorption properties are attributed to the conductive loss and dielectric loss mainly caused by the higher oxygen vacancy concentration of CeO₂ in RGO/CeO₂, which is demonstrated by X-ray photoelectron spectroscopy. Moreover, multiple interfacial polarizations occurring in the multi-interfaces between CeO₂ and RGO sheets may be beneficial to microwave absorption. RGO/CeO₂ could be used as an attractive candidate for the new type of microwave absorptive materials.

BiOI/HZSM-5 composites were synthesized via a facile and environmentally-benign hydrothermal method. The crystalline structures and morphologies of the powder have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activity of samples was tested for degradation of methylene blue (MB) and Rhodamine B (RhB) dye under simulated solar light irradiation. The degradation rate of MB and RhB by BiOI/HZSM-5 composite photocatalysts respective reach 99.6% and 98.6% under visible light irradiation, BiOI/HZSM-5 exhibited the highest photocatalytic performance when compared with pure BiOI.

Ultraviolet (UV) detection characteristics of Ag Schottky contacts with ZnO nanorods (ZnO-NRs) grown on Indium Tin Oxide (ITO)-coated glass substrates have been investigated. A low-temperature hydrothermal method was used for growing ZnO-NRs. Circular contacts of Ag were deposited above the ZnO-NRs/ITO samples using the shadow mask technique. The structural properties of the ZnO-NRs were characterized by using scanning electron microscopy (SEM), atomic force microscope (AFM) and X-ray diffraction (XRD). The results revealed a (0002) crystal orientation and a wurtzite hexagonal structure. The electrical characteristics of the Ag/ZnO-NR Schottky contacts were studied at forward applied bias over the range 0V to 1V, under dark and UV illumination. The dark and photocurrents were $1.29\times 10^{-5}$A and $2.16\times 10^{-5}$A, respectively, and the contrast ratio (ratio of photocurrent to dark current) was 1.67 at $+$1.0V for these devices. The results show that these devices could be useful for cost-effective and low-voltage UV detection applications.

In this study, direct Z-scheme MnWO₄/g-C₃N₄ photocatalyst was fabricated via facile hydrothermal method. Compared with pristine graphitic carbon nitride (g-C₃N₄) and manganous tungstate (MnWO₄), the prepared MnWO₄/g-C₃N₄ photocatalyst showed obviously enhanced photocatalytic activity for Rhodamine B (RhB) degradation under visible light irradiation. The MnWO₄/g-C₃N₄ photocatalyst prepared with 10% MnWO₄ (MC10%) showed the highest photocatalytic activity among all samples, which is about 2.3 and 12.7 times than that of pristine g-C₃N₄ and MnWO₄, respectively. This enhancement is due to the strong light absorption and efficient electron–hole separation of direct Z-scheme MnWO₄/g-C₃N₄ photocatalyst. Electron spin resonance (ESR) experiments and active species trapping experiments revealed that $•$OH and $•{\mathrm{\text{O}}}_2^{-}$ are the main active species in the photocatalytic process. This work may be beneficial for designing MnWO₄-based Z-scheme photocatalyst for application in environmental remediation.

In this work, we report theoretical and experimental study of Pd/ZnO nanorod (NR) Schottky diodes-based ultraviolet photodetector (UV-PD). The ZnO-NRs are deposited on indium tin oxide (ITO) coated glass substrates by using a low-temperature hydrothermal method. The surface morphology of the ZnO-NRs film is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The SEM image shows vertically grown NRs with uniformity, and XRD shows the preferred (002) orientation of ZnO-NR films. The current–voltage characteristics of Pd/ZnO-NR Schottky diodes are studied under dark and UV light. A voltage bias from $-$1V to $+$1V is applied and the ratio of photocurrent to dark current was ($\sim 0.17\times 10^2$ at $V=0.5$V) calculated from the $I$–$V$ curve. The value of responsivity was found to be 0.111A/W at $\lambda =365$nm and at $\mathrm{\text{bias}}=0.50$V. An approximated UV-PD structure has also been numerically simulated using three-dimensional (3D) device simulator from Visual TCAD of Cogenda International. The simulated $I$–$V$ characteristics have also been plotted under both dark and light conditions. The simulated results are found to be following the nature of experimental results.

Nanostructure-based resistive switching memory devices are being developed for low power, multilevel storage capability, extended retention capacity, and scalable devices. The zinc tungstate (ZnWO${}_4)$ nanoparticle was prepared via the facile hydrothermal method. The X-ray diffraction technique confirmed ZnWO₄ monoclinic phase and crystallite nature. The scanning electron microscope was used to identify the rod-like ZnWO₄ nanostructure, and further, the lattice orientation was investigated by high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy confirmed the binding states with composition of ZnWO₄. Resistive switching memory based on ZnWO₄ was produced and resulted in low-operating voltage.

A two-step low-temperature hydrothermal method was used to construct an aluminum-nickel compound network structure on the substrate surface, followed by a secondary hydrothermal synthesis of ZnO nanorod array. After low surface energy material modification, a superhydrophobic and superoleophobic surface was obtained. The aluminum-nickel compound network structure plays a key guiding role in the growth of ZnO nanorod arrays. The uniformly shaped and densely arranged ZnO nanorod arrays have high roughness and exhibit excellent hydrophobic properties after modification. The surface of the ZnO nanorod array is improved in terms of UV resistance due to the size effect. The effects of hydrothermal reaction temperature, hydrothermal reaction time, hydrothermal reaction pH value, and Zn${}^{2+}$ concentration on the surface structure, morphology, and properties of the ZnO nanorod array were also studied.