MoS2 quantum dots@TiO2 nanotube composites with enhanced photoexcited charge separation and high-efficiency visible-light driven photocatalysis

Thermal Treatment of Polyvinyl Alcohol for Coupling MoS2 and TiO2 Nanotube Arrays toward Enhancing Photoelectrochemical Water Splitting Performance

Solar-driven photoelectrochemical (PEC) water splitting, using semiconductor photoelectrodes, is considered a promising renewable energy source and solution for environmental sustainability. Herein, we report polyvinyl alcohol (PVA) as a binder material for combining MoS2 and TiO2 nanotube arrays (TNAs) to improve PEC water splitting ability. By a thermal treatment process, the formation of the π conjunction in the PVA structure enhanced the PEC performance of MoS2/TNAs, exhibiting linear sweeps in an anodic direction with the current density over 65 μA/cm2 at 0 V vs. Ag/AgCl. Besides, the photoresponse ability of MoS2/TNAs is approximately 6-fold more significant than that of individual TNAs. Moreover, a Tafel slope of 140.6 mV/decade has been obtained for the oxygen evolution reaction (OER) of MoS2/TNAs materials.

Efficient photocatalytic H2production realized by MnxCd1-xSeIn situheterojunction

Fast recombination of photoinduced carriers inhibits the performance of photocatalysts. By constructing heterojunctions, built-in electric fields can be formed to separate electrons and holes and finally enhance the photocatalytic efficiency. Herein, a Mn_xCd_1-xSein situheterojunction was fabricated by a facile solvothermal method to draw upon this advantage. Absorption spectra show that the light absorption of CdSe raises up obviously after the doping of Mn²⁺. Best performance was achieved when the doping percent of Mn²⁺was 50%. This Mn_0.5Cd_0.5Se sample exhibits a 7.2 folds increase in hydrogen evolution against pure CdSe owing to the fast electron transportation. Moreover, it proves well stability in an 18 h cycling test and gains a 6.7% apparent quantum yield under 420 nm light. In summary, this work constructs anin situheterojunction to enhance the photocatalytic hydrogen evolution efficiency and sheds light on a feasible way for the application of photocatalysis.

In Situ Growth of Metallic 1T-MoS2 on TiO2 Nanotubes with Improved Photocatalytic Performance

1T-MoS₂ is in situ grown on TiO₂ nanotubes (TNTs) using a hydrothermal method, forming a 1T-MoS₂@TNTs composite, which is confirmed by its physical characterization. The prepared composites show enhanced photocatalytic performance for the degradation of tetracycline hydrochloride under visible light, and the improved photocatalytic activity is closely related to the loaded amount of 1T-MoS₂. Therein, 0.5 wt % 1T-MoS₂@TNTs can degrade 57% in 1 h, which is the highest photocatalytic efficiency observed in experiments so far. It is speculated that the introduction of 1T-MoS₂ may optimize light absorption and charge separation/transport. The active species are identified and the reaction mechanism is proposed here.

One-step hydrothermal synthesis of a ternary heterojunction g-C3N4/Bi2S3/In2S3 photocatalyst and its enhanced photocatalytic performance

In recent years, photoelectrocatalysis has been one of the hotspots of research. Graphite-like carbon nitride (g-C3N4) is one of the few non-metal semiconductors known and has good potential in the field of photocatalysis due to its simple preparation method and visible light effects. In this study, a method for compounding two semiconductor materials, In2S3 and Bi2S3, on the surface of g-C3N4 via a one-step hydrothermal method is reported, and it was found that this resulting material showed remarkable properties. The advantages of this method are as follows: (1) the formation of a heterojunction, which accelerates the separation efficiency of photogenerated carriers; (2) a large number of holes and defects on the surface of g-C3N4 are conducive to the nucleation, crystallisation and growth of In2S3 and Bi2S3. Compared with its counterpart catalysts, the CN/In2S3/Bi2S3 composite catalyst has significantly improved performance. Due to its high degree of crystallinity, the adsorption capacity of the catalyst itself is also significantly improved. In addition, the stability of the composite material maintains 90.9% after four cycles of use, and the structure is not damaged. In summary, CN/Bi2S3/In2S3 composite materials are believed to have broad application potential in the treatment of dye wastewater.

TiO2 anchored on MoS2 nanosheets based on molybdenite exfoliation as an efficient cathode for enhanced Cr (VI) reduction in microbial fuel cell

MoS₂ nanosheet-decorated TiO₂ nanocomposites were prepared via facile liquid-phase exfoliation of natural molybdenite combined with in situ hydrolysis route. These materials were used as a photocathode for the first time in microbial fuel cell (MFC) to reduce hexavalent chromium (Cr (VI)). Results showed the maximum power density of 1 wt% MoS₂/TiO₂-based MFC was 3.7 and 1.9 times higher than that of blank graphite and TiO₂-based MFC, respectively. This MFC achieved 99.57% removal of Cr (VI) with a concentration of 20 mg L^-1 within 8 h under visible light illumination at pH 2 and high degradation rate of 2.49 g m^-3 h^-1. The introduction of MoS₂ nanosheets as a cocatalyst can expand the absorption of visible light, thereby leading to increased electronic participation in Cr (VI) reduction. Moreover, the appropriate amounts of MoS₂ nanosheets also contribute to electrons migration and additional active site. The enhanced power output and Cr (VI) reduction efficiency of MFC can be attributed to the synergistic coupling between bioanode and MoS₂/TiO₂ photocathode. On the basis of its facile and scalable synthetic strategy as well as its stable and outstanding photoelectrocatalytic performance for MFC, this MoS₂/TiO₂ nanocomposite showed potential in the efficient treatment of wastewater.

A novel ternary MoS2/MoO3/TiO2 composite for fast photocatalytic degradation of rhodamine B under visible-light irradiation

In this article, novel ternary MoS₂/MoO₃/TiO₂ composite catalysts were developed.

A phenol phosphorescent microsensor of mesoporous molecularly imprinted polymers

Based on the optical quenching phenomenon, a smart mesoporous phosphorescent microsensor was built. It is a phenol microsensor, which inherits a high selectivity of molecularly imprinted polymers (MIPs) and room-temperature phosphorescence (RTP) properties of Mn-doped ZnS quantum dots (QDs). On the surface of silane-modified Mn-doped ZnS QDs, the phenol microsensor was synthesized by a sol–gel process. Because of the presence of a porogenic agent, a mesoporous structure played an important role in increasing the detection sensitivity. The MPTS-modified Mn-doped ZnS QDs were used as solid supports and auxiliary monomers. Under optimal conditions, the experiment for the detection of phenol had a linear range of 5.0 to 50 μmol L⁻¹ with a correlation coefficient of 0.9983 and a high imprinting factor (IF) of 3.28. In addition, the as-prepared Mn-doped ZnS QD@ms-MIPs were successfully applied for phenol determination and selectivity in water samples. Therefore, this study provides a highly selective and sensitive mesoporous phosphorescent microsensor for the detection of phenol.

Based on the optical quenching phenomenon, a smart mesoporous phosphorescent microsensor was built.

A fluorescent microsensor for the selective detection of bifenthrin

Based on the fluorescence quenching phenomenon, a smart fluorescent microsensor was synthesized. The bifenthrin (BI) microsensor inherited the high selectivity of molecular imprinted polymers (MIPs) and the excellent fluorescence properties of aqueous CdTe quantum dots (QDs). Aqueous CdTe QDs are functionalized by octadecyl-4-vinylbenzyl-dimethyl-ammonium chloride (OVDAC). A type of functional monomer, 4-vinylphenylboronic acid (VPBA), was used and its boronic acid groups could covalently combine with a cis-diol compound for direct imprinting polymerization. The OVDAC-functionalized aqueous CdTe QDs were used as solid supports and auxiliary monomers. Under optimal conditions, experimentation showed that BI had a linear detection range of 10 to 300 μmol L⁻¹ with a correlation coefficient of 0.9968 and a high imprinting factor (IF) of 4.53. In addition, the prepared MIP-OVDAC/CdTe QDs were successfully used to detect BI in water samples. Therefore, this work provided a highly selective and sensitive fluorescence probe for the detection of BI. In addition, the fluorescence probe could be used to detect other targets by changing the functional monomers.

Based on the fluorescence quenching phenomenon, a smart fluorescent microsensor was synthesized.

Insights into the TiO2-Based Photocatalytic Systems and Their Mechanisms

Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H2 production, CO2 reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO2 is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO2 photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO2 photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO2 such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO2 that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO2 makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H2 production, CO2 conversion, etc. For these reasons, TiO2 can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO2 in terms of its modifications towards multifunctional photocatalytic applications.

Facile synthesis of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) nanosheets for DFT supported visible photocatalysis of 2-Chlorophenol

Visible light active g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) ternary composite nanosheets were fabricated by facile co-precipitation routes. The density functional theory (DFT) computations investigated changes in geometry and electronic character of g-C3N4 with CeO2 and Fe3O4 addition. Chemical and surface characterizations were explored with XRD, XPS, SEM, TEM, PL, DRS and Raman measurements. DRS and PL spectroscopy evidenced the energy band gap tailoring from 2.68 eV for bulk g-C3N4 and 2.92 eV for CeO2 to 2.45 eV for the ternary nanocomposite. Efficient electron/hole pair separation, increase in red-ox species and high exploitation of solar spectrum due to band gap tailoring lead to higher degradation efficiency of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01). Superior sun light photocatalytic breakdown of 2-Chlorophenol was observed with g-C3N4 having CeO2 loading up to 5 wt%. In case of ternary nanocomposites deposition of 1 wt% Fe3O4 over g-C3N4/CeO2 binary composite not only showed increment in visible light catalysis as predicted by the DFT studies, but also facilitated magnetic recovery. The g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) nanosheets showed complete mineralization of 25 mg.L-1 2-CP(aq) within 180 min exposure to visible portion of sun light and retained its high activity for 3 consecutive reuse cycles. The free radical scavenging showed superoxide ions and holes played a significant role compared to hydroxyl free radicals while chromatographic studies helped establish the 2-CP degradation mechanism. The kinetics investigations revealed 2.55 and 4.04 times increased rate of reactions compared to pristine Fe3O4 and CeO2, showing highest rate constant value of 18.2 × 10-3 min-1 for the ternary nanocomposite. We present very persuasive results that can be beneficial for exploration of further potential of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) in advance wastewater treatment systems.

Hydrothermal synthesis of MoS2 nanosheet loaded TiO2 nanoarrays for enhanced visible light photocatalytic applications

A molybdenum disulfide (MoS₂) nanosheet-decorated titanium dioxide (TiO₂) NRA heterojunction composite was fabricated successfully through a two-step hydrothermal approach. Microstructures and optical properties of specimens were characterized by field-emission scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy. The gaps of the TiO₂ nanorods have been filled with tiny MoS₂ nanosheets, which can increase the surface area of MoS₂/TiO₂ NRA composite thin films. In addition, the photocatalytic activity of the thin films were measured and discussed in greater detail. The appropriate hydrothermal reaction temperature of MoS₂ is important for the growth of perfect MoS₂/TiO₂ NRA composites with significantly enhanced photocatalytic performance. The photodegradation rate and k value of MoS₂-220/TiO₂ are 86% and 0.0105 min⁻¹, respectively, which are much larger than those of blank TiO₂. The enhanced photocatalytic performance could be attributed to the higher visible light absorption and the reduced recombination rate of photogenerated electron–hole pairs.

A molybdenum disulfide (MoS₂) nanosheet-decorated titanium dioxide (TiO₂) NRA heterojunction composite was fabricated successfully through a two-step hydrothermal approach.

Visible-Light Driven TiO₂ Photocatalyst Coated with Graphene Quantum Dots of Tunable Nitrogen Doping

Nitrogen doped graphene quantum dots (NGQDs) were successfully prepared via a hydrothermal method using citric acid and urea as the carbon and nitrogen precursors, respectively. Due to different post-treatment processes, the obtained NGQDs with different surface modifications exhibited blue light emission, while their visible-light absorption was obviously different. To further understand the roles of nitrogen dopants and N-containing surface groups of NGQDs in the photocatalytic performance, their corresponding composites with TiO₂ were utilized to degrade RhB solutions under visible-light irradiation. A series of characterization and photocatalytic performance tests were carried out, which demonstrated that NGQDs play a significant role in enhancing visible-light driven photocatalytic activity and the carrier separation process. The enhanced photocatalytic activity of the NGQDs/TiO₂ composites can possibly be attributed to an enhanced visible light absorption ability, and an improved separation and transfer rate of photogenerated carriers.

Revealing the role of the 1T phase on the adsorption of organic dyes on MoS2 nanosheets

Herein, different phases of MoS₂ nanosheets were synthesized, characterized and tested for dye removal from water. The influence of the MoS₂ phases as well as the 1T concentration on the adsorption performance of organic dyes MO, RhB and MB was deeply investigated. The results revealed that the 1T-rich MoS₂ nanosheets have superior adsorption performance compared to other 2H and 3R phases. The kinetic results of the adsorption process demonstrate that the experimental data followed the pseudo-second order equation. Meanwhile, the adsorption of dyes over the obtained materials was fitted with several isotherm models. The Langmuir model gives the best fitting to the experimental data with maximum a adsorption capacity of 787 mg g⁻¹. The obtained capacity is significantly higher than that of all previous reports for similar MoS₂ materials. Computational studies of the 2H and 1T/2H-MoS₂ phases showed that the structural defects present at the 1T/2H grain boundaries enhance the binding of hydroxide and carboxyl groups to the MoS₂ surface which in turn increase the adsorption properties of the 1T/2H-MoS₂ phase.

The high adsorption capacity of dyes onto the 1T-rich MoS₂ samples is due to the strong binding between the hydroxide/carboxyl groups and the 1T active sites. The capacity can be tuned by controlling the ratio between 1T and 2H phases of MoS₂ nanosheets.