Efficient visible light photodegradation of Methylene blue using TiO 2 -graphene based composites has been reported. DFT calculations corroborate the mechanism for Ti-O-C bond formation, leading to an additional band edge and band gap tuning.
AbstractHere we report experimental and theoretical study of two TiO 2 -graphene oxide (TG) and TiO 2 -reduced graphene oxide (TR) composites synthesized by a facile and ecological route, for enhanced visible light (~470nm) photocatalyc degradation of Methylene Blue (MB) (99% efficiency), with high rate constant value (1800% over bare TiO 2 ). TG couples TiO 2 nanopowder with Graphene Oxide (GO) while TR couples it with reduced graphene oxide (RGO). The present study, unlike previous reports, discusses never before reported double absorption edges obtained for both TG (3.51 eV and 2.51 eV) and TR (3.42 eV and 2.39 eV) composites, which marks the reason behind feasible visible light (2.56 eV) induced photocatalysis. TiO 2 domains in the composites dominate the higher band edge, while GO/RGO domains explain the lower band edge. Formation of Ti-O-C bond in both TG and TR drives the shifting up of the valence band edge and reduction in band gap. Further, these bonds provide a conductive pathway for charge carriers from TiO 2 nanopowder to the degrading species via the GO/RGO matrix, resulting in decreased charge carrier recombination in TiO 2 and enhanced efficiency.To attest that the developed theory is proof-positive, density function theory (DFT) calculations were performed. DFT obtained energetics and electronic structures support experimental findings by showcasing the play of Ti-O-C bond, resulting in double band edge phenomenon in composites.Finally, the mechanism behind MB degradation is discussed comprehensively and the effect of weight percent of GO/RGO in composite on rate constant and photodegradation efficiency has been studied experimentally and explained by developing analytical equations. 4 promising as it simultaneously possesses excellent absorptivity, transparency, conductivity and reachability, which could assist effective photodegradation of pollutants.There is a pool of reports showing the enhanced photocatalytic activity of TiO 2 nanoparticles with graphene composites for the degradation of organic molecules and photocatalytic splitting of water under UV light. 22, 28-38 Enhanced photocatalytic activity was attributed to the synergetic effect between graphene and TiO 2 nanoparticles, because graphene acts as an excellent electron acceptor and transporter, the Ti-O-C bond open up an easy path for charge transfer which remarkably decreases the recombination of electron−hole pairs. 3 Although claiming good efficiency, many of these reports are based on usage of un-ecological UV light and suffer from low kinetics (k value). [28][29][30] Realizing the importance of efficient visible light photodegradation, there are few reportes which show enhanced photocatalytic activity of TiO 2 -GO/RGO composites under visible light. 39-42 The results and application part is...
Most
of the reports suggest that liquid exfoliated WS2-QDs are
unstable; therefore the need of present day is to develop
a novel synthesis route for producing long-term stable WS2-QDs. Herein, we report a bottom-up single-step hydrothermal growth
of in situ functionalized blue fluorescent WS2-QDs with
stable fluorescence in aqueous media without subsequent treatments.
Presence of various functional groups over the surface of f-WS2-QDs provides high solubility and stability to f-WS2-QDs in aqueous media preserving its fluorescence. Further, photoluminescence
property of f-WS2-QDs has been employed to devise an optical
sensor with a high sensitivity (K
D ∼
104 M–1) and selectivity for ferric (Fe3+) ions. Under the optimal condition, response of the sensor
is found to be linear in the range of 0–55 μM with a
limit of detection (LOD) of 1.32 μM, which is within the maximum
permissible level of Fe3+ (∼5.4 μM) in human
drinking water by the USEPA. Further, we have also carried out a detailed
evaluation on fluorescence quenching kinetics of f-WS2-QDs.
Nonlinear behavior of S–V plot and TRPL measurements suggest
that quenching is a mixed phenomenon of dynamic as well as static
processes. Finally we have proposed a mechanism for fluorescence quenching
of f-WS2-QDs in the presence of Fe3+.
Mesoporous silica particle-embedded graphene oxide (GO) is a promising platform for electrochemical biosensing. We report a GO–SiO2 composite electrode for urea detection, with excellent reproducibility, specificity and stability.
The proposed immunosensor based on in situ grown gold decorated reduced graphene oxide exhibits superior sensing performance towards food toxin detection.
Supported lipid bilayers
on solid surfaces have promising potential
for diverse applications, such as separation processes, biosensors,
drug delivery, and more. However, the self-assembly of supported lipid
bilayers via vesicle fusionthe commonly used preparation method
for these lipid bilayersis not fully understood. It is often
found that lipid bilayers are patchy or exhibit holes/defects, which
may hinder their applicability. Moreover, it is not fully understood
whether these holes are transient, kinetically trapped, or thermodynamically
stable (long-lasting). Here, we derived equations to quantitatively describe the mechanism of vesicle fusion on atomically smooth hydrophilic
surfaces. The derived equations determine whether defectless lipid
bilayers are thermodynamically stable/favorable and qualitatively predict the self-assembly rate. It is shown that vesicle fusion
is governed by van der Waals and double layer interactions, as well
as undulation repulsion between the lipid bilayers and the solid surface.
Utilizing various experimental techniques, we confirmed the equation
predictions by studying the self-assembly of lipid bilayers on silicon
wafers using lipid mixtures that exhibited different electric potentials.
Furthermore, we found that cholesterol increases the lipid bilayer
resistivitya crucial parameter for several applicationsand
the rate of self-assembly, by decreasing both the dielectric constant
of the lipid bilayer and the undulation repulsion between the lipid
bilayers and the solid surface. The derived equations can be used
as quantitative guidelines for designing supported lipid structures
on the surface, such as a layer of intact lipid vesicles, patchy or
defectless lipid bilayers.
Silica
scaling of membranes used in reverse osmosis desalination
processes is a severe problem, especially during the desalination
of brackish groundwater due to high silica concentrations. This problem
limits the water supply in inland arid and semiarid regions. Here,
we investigated the influence of surface-exposed organic functional
groups on silica precipitation and scaling. A test solution simulating
the mineral content of brackish groundwater desalination brine at
75% recovery was used. The mass and chemical composition of the precipitated
silica was monitored using a quartz crystal microbalance, X-ray photoelectron
spectroscopy, and infrared spectroscopy, showing that surfaces with
positively charged groups induced rapid silica precipitation, and
the rate of silica precipitation followed the order −NH2 ∼ −N+(CH3)3 > −NH2/–COOH > −H2PO3 ∼ −OH > −COOH > −CH3. Force vs distance AFM measurements showed that the adhesion
energy
between a silica colloid glued to AFM cantilever and the studied surfaces
increased as the surface charge changed from negative to positive.
Thus, for the first time direct measurements of molecular forces and
specific chemical groups that govern silica scaling during brackish
water desalination is reported here. The influence of the different
functional groups and the effect of the surface charge on silica precipitation
that were found here can be used to design membranes that resist silica
scaling in membrane-based desalination processes.
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