Removing toxic organic dyes from wastewater is a growing environmental challenge, and the development of efficient, stable, sustainable, and reusable photocatalysts holds great significance. This study develops a novel sustainable Molybdenum Disulfide/Polyacrylamide (MoS2/PAM) composite hydrogel by incorporating the photocatalytic activity of MoS2 nanosheets with the porous, water-swelling properties of a PAM hydrogel matrix. Structural characterizations confirmed the successful integration of MoS2 into PAM hydrogel. The X-ray Diffraction (XRD) analysis revealed the amorphous nature of PAM and the distinct (002) diffraction peak of MoS2 in the composite. Furthermore, Raman and morphological analysis demonstrated the uniform distribution of MoS2 nanoflakes on the hydrogel porous network. This hybrid structure enhanced surface-active sites, light harvesting, and significant dye adsorption. Photodegradation experiments demonstrated a notable improvement in catalytic performance, with the rate constant increasing from 0.0049 min-1 for PAM to 0.020 min-1 for the MoS2/PAM hydrogel, resulting in 93 % degradation of the 4 mu M crystal violet (CV) dye within 110 min under visible light. Beyond efficiency, the hydrogel solid framework facilitates easy separation from treated water, thereby avoiding secondary contamination, a major drawback of conventional photocatalysts. Furthermore, the composite-maintained stability and reusability up to several cycles. These results highlight the MoS2/PAM hydrogel as a cost-effective, durable, and environment friendly photocatalyst for sustainable wastewater treatment.

In this article, highly fluorescent phosphorus(V) corrole was synthesised which was then combined with CdSe quantum dots (QDs) in order to study Förster resonance energy transfer (FRET) mechanism between CdSe QDs (donor) and phosphorus corrole (acceptor). Spectral overlap between QD's emission profile and corrole's absorption profile was found to be significant enough to result into Förster resonance energy transfer (FRET). The UV-vis spectrum experienced increase in the absorption bands on addition of phosphorus corrole to CdSe QDs suggesting QD-corrole conjugation. In the steady state fluorescence measurements, emission spectrum observed quenching in the fluorescence intensity of prepared CdSe QDs on addition of phosphorus corrole. Likewise, in case of time-resolved fluorescence measurements it was noticed that the CdSe QD's lifetime was greatly quenched by the presence of a corrole acceptor. Stern-Volmer plot was made to show quenching in this case was dynamic in nature. Based on the results of UV-vis, steady state and time-resolved fluorescence measurements the plausible mechanism behind such observations is considered to be FRET.

Cobalt-doped and undoped zinc oxide (ZnO) nanoparticles (NPs) with different dopant concentrations were synthesized via the sol-gel method. The structural, morphological, and optical properties of the synthesized NPs were investigated using various techniques. The NPs exhibit a wurtzite structure with an average crystallite size of 20-34 nm. Change in photoluminescence (PL) spectra from dual to single band with dopants suggested decreasing surface state contribution. The PL lifetime of the 430 nm band is too short (< 10 ps), where it is multi-exponential and significantly large for the 550 nm band with a major contribution of 0.3-1.0 ns and a minor contribution of 7-9 ns and 119-126 ns. The photocatalytic performance of NPs was examined by decomposing a Congo red dye under dark, white (LED) light and UV irradiation. Among all the doped NPs, 20% Co(2+ )doped ZnO shows superior photocatalytic activity for dye degradation with a faster reaction rate constant.

The molybdenum disulfide (MoS2) with its visible energy bandgap plays a vital role in treating wastewater from organic pollutants through the photocatalytic process. Here, the one-pot hydrothermal method demonstrates the facile synthesis of the 2H phase of MoS2 nanosheets. The structural and chemical compositional analysis of the nanosheets were performed by the X-ray diffraction (XRD) pattern and FT-IR spectrum, respectively. Morphological analysis of the MoS2 nanosheets was done by the scanning electron microscope (SEM) and high-resolution transmission electron microscope (HR-TEM). The UV-visible absorption spectroscopy was used to examine the catalyst (MoS2) optical properties along with the photodegradation process of the crystal violet (CV) dye. Degradation efficiency is estimated at different concentrations of nanosheets and under different illuminations. The degradation process of the dye follows pseudo-first-order kinetics. Thus, the decomposition of the harmful industrial dye waste in the water is essential for the survival of humanity and aquatic life in the ecosystem. (C) 2021 Elsevier B.V. All rights reserved.

Three different phases, namely anatase, mixed and rutile phases of TiO2 nanoparticles (NPs) were developed with varying temperatures from 400 to 900 degrees C and confirmed using various characterization techniques. The XRD analysis of TiO2 NPs in temperature range of 290 to 77 K with no significant changes predict the thermally stable NPs. Photoinduced carrier dynamics of TiO2 NPs were investigated by the temperature dependence (TD) photoluminescence (PL) and TD time-resolved PL (TRPL) decays. With varying temperatures from 290 to 77 K, the anatase phase exhibits an additional and dominant 530 nm PL band. However, the mixed and rutile phases show three well-resolved PL bands, including 420 nm, 530 nm and near-infrared (NIR) bands at 820 nm at a lower temperature. Again, 530 nm band dominated for mixed-phase. In contrast, for the rutile phase, the 820 nm band dominated at <100 K. The PL lifetime of the 420 nm band is nearly a single exponential for all the phases. And is also true for the 530 and 820 nm PL bands, but biexponential for <= 100 K. Both the PL and TRPL results predict the presence of trap states in TiO2 NPs for anatase and rutile phases. The PL is originated due to donor-acceptor recombination, whereas oxygen vacancies served as donor and hydroxyl groups serve as accepter sites. The NIR band is attributed to the trapped electrons in rutile TiO2, which recombine with free holes and intrinsic defects. Also, the trapped electrons were generated in one of two ways: direct trapping or trap-to-trap hopping. The carrier dynamic in NPs depends on the trap states as the photoexcited carriers transfer into surface sites which competes with non-radiative and radiative recombinations during the relaxation process. Thus, the findings show that the trap states in TiO2 can significantly influence TiO2 photocatalytic activity when exposed to appropriate light.

Two-dimensional (2D) layered MoS2 nanosheets (NSs) possess many unique properties and hold great potential for various applications. Herein, MoS2 NSs were synthesized by a hydrothermal method. The as-synthesized MoS2 NSs are crystalline and layered. Absorption and electroabsorption (E-A) spectra of MoS2 doped in a poly(methyl methacrylate) (PMMA) thin film were measured at different temperatures (290-40 K). The E-A spectra detected at the second harmonic of the modulation frequency of the applied electric field were analyzed using an integral method by considering the Stark effect as a dominant feature. The absorption spectra consist of seven transitions, among which five transitions are contributed to the E-A spectra. It is found that the changes in the electric dipole moment and polarizability of each transition determined at different temperatures increase substantially with decreasing temperature. Electronic resonance states identified for low-energy excitonic bands of MoS(2 )NSs showed prominence E-A signals. The study is essential to understand the electronic structure in the photoexcited state, which is important for applications of MoS2 NSs to optoelectronic devices.

Transition metal ions (Ag+, Cu2+, and Ni2+) doped and undoped TiO2 nanoparticles (NPs) were synthesized via cost effective sol-gel method with 1.0 wt% dopant concentration. The microstructure and chemical compositions of these NPs were examined using various techniques such as x-ray diffractometry, field emission scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared and absorption and photoluminescence (PL) spectroscopy. The average size of the NPs is in the range of 10-20 nm and lattice spacing is 0.36 nm corresponding (101) plane. The absorption and photoluminescence (PL)-excitation spectra of metal-doped TiO2 NPs are shifted to the longer wavelength region, which indicates reduced bandgap than the bare TiO2 NPs. The absorption and PL spectra of methylene blue (MB) in the presence of undoped and metal ions doped TiO2 NPs show dramatic changes upon UV-irradiation. The absolute absorption intensity reduced entirely and the solution of MB became colorless in the presence of UV irradiation. The PL of the degraded dye exhibits a new band in the shorter wavelength region, which has a multi-exponential decay function and an increased average PL lifetime. Among all the samples, Cu2+ ions-doped TiO2 NPs shows the superior photocatalytic activity for the degradation of dye and followed pseudo-first-order kinetics.

Titanium dioxide (TiO2) nanoparticles (NPs) were prepared by the sol-gel method with titanium isopropoxide as a precursor at different annealing temperatures. The analysed X-ray diffraction (XRD) patterns, Raman and Fourier transform infrared spectra characteristics demonstrated the structural transformation from amorphous to anatase and further to rutile phase while increasing annealing temperature. In addition, a mixed phase of TiO2 NPs is formed, which consists of both the phases. The absorption and photoluminescence (PL) spectra of mixed and rutile phases are shifted towards longer wavelength region. Furthermore, the photocatalytic performance of the different type of TiO2 NPs was examined through the degradation of a dye, rhodamine B (RhB) under UV radiation, and by measuring changes in absorption and PL spectra. The anatase phase structure shows higher photocatalytic activity than the rutile phase. However, the mix phase has the highest photocatalytic activity among all the structures, which degraded RhB entirely with a faster rate. On the other hand, the rutile phase is unable to take part in this process. Thus, the mix phase of TiO2 NPs is highly useful for industrial and environmental applications.