Ceria-doped SnO2 nanocubes for solar light-driven photocatalytic hydrogen production.

The photocatalytic generation of hydrogen via solar energy using metal oxide semiconductor catalysts is a clean and renewable process which has the potential of solving the current energy nexus. SnO2 is one such well-studied and established photocatalyst currently in practice but is only ultraviolet-light active which accounts for only 4% of the total incoming solar energy. The current study focuses on bringing this SnO2 into the visible range using ceria as a dopant. Sol-gel and combustion methods were employed for synthesis and the as-synthesized catalysts were characterized using XRD, BET, UV diffuse reflectance spectra, PL spectra, and SEM micrographs. A unique cuboid type morphology was observed in 6% ceria-doped SnO2 which provided more active sites for light absorption and thus reported a remarkable hydrogen production rate of 1.978 mmol/h under sunlight which was almost 346 times that of pure SnO2 (5.71 µmol/h). Photoluminescence spectra of ceria-doped SnO2 showed lower peak positions as compared to the pure SnO2 indicating a reduction in charge recombination and an increase in the life time of the active species which explains the enhanced hydrogen production rates. The recyclability study of the catalysts showed that the hydrogen amount produced in the fifth recycle was nearly 80% as the first cycle showing that the catalyst can be used very effectively for more than five cycles without compromising on the yield.

Preparation, Characterization, and Evaluation of Emission and Performance Characteristics of Thumba Methyl Ester (Biodiesel).

Thumba oil with a higher triglyceride content can be a promising feed for synthesizing a fatty acid alkyl ester as an alternative to pure diesel. The current study investigates the emission and performance characteristics of thumba methyl ester (TME) in compression ignition (CI) engines corresponding to variable loads and compression ratios (CRs), respectively. TME was prepared at an optimized pressure of 5 bar by hydrodynamic cavitation. The properties of TME-diesel blends with varied volume percentages of biodiesel, such as 5, 10, 15, 20, and 25, denoted B5, B10, B15, B20, and B25, respectively, were compared to pure TME (100% biodiesel) and pure diesel (100%). The B20 biodiesel blend has been observed as the optimal one based on the lower emission composition and higher brake thermal efficiency. For B20 fuel, injection at 23° before the top dead center (TDC) and a CR of 18 resulted in the lowest brake specific fuel consumption of 0.32 kg/kW h and a maximum brake thermal efficiency of 36.5%. Using titanium dioxide nanoparticles in the pre-stage of TME manufacturing has ultimately reduced the nitrogen oxide, hydrocarbon, and carbon monoxide emissions. At a CR of 18 and advanced injection 23° before TDC for a CI engine, TME derived from thumba oil has the potential to be a viable diesel substitute.

Effect of Defects on Optical, Electronic, and Interface Properties of NiO/SnO2 Heterostructures: Dual-Functional Solar Photocatalytic H2 Production and RhB Degradation.

Photocatalytic H2 evolution and organic pollutant oxidation have witnessed a radical surge in recent times. However, this integration demands spatial charge separation and unique interface properties for a trade-off between oxidation and reduction reactions. In the current work, defect engineering of NiO/SnO2 nanoparticles aided in altering the optoelectronics and interface properties and enhanced photocatalytic activity. After annealing the catalysts in a N2 atmosphere, the hydroxyl groups were replaced by water molecules through surface modification. The photoexcited holes accumulated on SnO2 break the water molecules and facilitate the reduction of protons on NiO; this is known as spatial separation. Meanwhile, direct hole oxidation, an oxygen reduction reaction, ensures the degradation activity in this 2-fold system. By defect engineering, the limitations of SnO2 such as higher H2O adsorption, wide bandgap (reduced from 3.02 to 1.88 eV), and electronic properties were addressed. The H2 production in the current work has attained a value of 3732 µmol/(g h), which is 2.9 times that of the previous best reported under sunlight. Recyclability tests confirmed the stability of vacancies by promoting the reoxidation of defect states during photocatalytic activity. Additionally, efforts were made to study the effect of defect density on the photocurrent, the electrical resistance, and the mechanism of photocatalytic reactions. Electrochemical characterizations, UPS, XPS, UV-DRS, and PL were employed to understand the influence of defects on the bandgap, charge recombination, charge transport, charge carrier lifetime, and the interface properties that are responsible for photocatalytic activity. In this regard, it was understood that maintaining the optimal defect concentration is important for higher photocatalytic efficiencies, as the defect optimality preserves key photocatalytic properties. Apart from characterizations, the photocatalytic results suggest that excess defect density triggers the undesired thermodynamically favored back reactions, which greatly hampered the H2 yield of the process.

Light-induced modulation of DNA recognition by the Rad4/XPC damage sensor protein.

Biomolecular structural changes upon binding/unbinding are key to their functions. However, characterization of such dynamical processes is difficult as it requires ways to rapidly and specifically trigger the assembly/disassembly as well as ways to monitor the resulting changes over time. Recently, various chemical strategies have been developed to use light to trigger changes in oligonucleotide structures, and thereby their activities. Here we report that photocleavable DNA can be used to modulate the DNA binding of the Rad4/XPC DNA repair complex using light. Rad4/XPC specifically recognizes diverse helix-destabilizing/distorting lesions including bulky organic adduct lesions and functions as a key initiator for the eukaryotic nucleotide excision repair (NER) pathway. We show that the 6-nitropiperonyloxymethyl (NPOM)-modified DNA is recognized by the Rad4 protein as a specific substrate and that the specific binding can be abolished by light-induced cleavage of the NPOM group from DNA in a dose-dependent manner. Fluorescence lifetime-based analyses of the DNA conformations suggest that free NPOM-DNA retains B-DNA-like conformations despite its bulky NPOM adduct, but Rad4-binding causes it to be heterogeneously distorted. Subsequent extensive conformational searches and molecular dynamics simulations demonstrate that NPOM in DNA can be housed in the major groove of the DNA, with stacking interactions among the nucleotide pairs remaining largely unperturbed and thus retaining overall B-DNA conformation. Our work suggests that photoactivable DNA may be used as a DNA lesion surrogate to study DNA repair mechanisms such as nucleotide excision repair.

Selection of suitable adsorbent for the removal of Cr(VI) by using objective based multiple attribute decision making method.

The objective of the current manuscript is to develop a systematic and simplified expert system for the selection of suitable adsorbent to treat Cr(VI). Selection of adsorbent among the large options available by considering all possible factors and their interaction is required in an easy, organized and rational way. In this study, fuzzy logic is used for the choosing an appropriate adsorbent for the Cr(VI) removal. Multiple attribute decision making (MADM) is utilized to work out the relative weighting values for the chosen sorbent. The preference index is calculated by using the subjective and objective weights. The normalized value associated with each parameter has given on the basis of effect of each parameter on the removal of Cr(VI) and uptake capacity of each material. The associated MADM method results and the barriers of the approach is mentioned to lay the basis for in addition enhancement.

Steering the Charge Kinetics in Dual-Functional Photocatalysis by Surface Dipole Moments and Band Edge Modulation: A Defect Study in TiO2-ZnS-rGO Composites.

Developing an efficient photocatalyst for concurrent hydrogen production and environmental remediation by using solar energy is a challenge. Defect engineering, although it offers a strategical promise to enhance the photocatalytic performance, has limitations that come from the ambiguity surrounding its role. In the current work, a comprehensive study on defects in promoting the charge transfer, band edge modulation, and surface reaction was carried out. The excess electrons springing from defects act like donor states and cause band bending at the junction interface. Characterization techniques such as X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, electron spin resonance, and photoluminescence were employed to investigate defect functionality, and its ultimate effect on photocatalytic performance was studied by simultaneous H2 production and methylene blue degradation. The role of graphene in optoelectronics and defect formation in the composite catalysts was explored. In addition, efforts have been made to unveil the reaction pathway for hydrogen evolution reaction and oxygen evolution reaction where excess defect density greatly hampered the quantum yield of the process. Results suggest that maintaining optimal defect concentration aborts the undesired thermodynamically favored back reactions. The conduction band and valence band values of the catalysts indicate that the photocatalytic mechanism was dominated by the electron pathway. Graphene acted as an effective electron sink when its concentration was around 2.5-3%. The superior activity of TiO2-ZnS-rGO was attributed to the narrow bandgap, rapid separation of photo-excited charge carriers, and favorable conduction band position for photocatalytic reactions. This work may assist in exploring the fundamental role of defects in driving the photocatalytic reactions and improve the selectivity in heterogeneous photocatalysis.

Monovalent ions modulate the flux through multiple folding pathways of an RNA pseudoknot.

The functions of RNA pseudoknots (PKs), which are minimal tertiary structural motifs and an integral part of several ribozymes and ribonucleoprotein complexes, are determined by their structure, stability, and dynamics. Therefore, it is important to elucidate the general principles governing their thermodynamics/folding mechanisms. Here, we combine laser temperature-jump experiments and coarse-grained simulations to determine the folding/unfolding pathways of VPK, a variant of the mouse mammary tumor virus (MMTV) PK involved in ribosomal frameshifting. Fluorescent nucleotide analogs (2-aminopurine and pyrrolocytidine) placed at different stem/loop positions in the PK serve as local probes allowing us to monitor the order of assembly of VPK that has two constituent hairpins with different intrinsic stabilities. We show that at 50 mM KCl, the dominant folding pathway populates only the more stable hairpin intermediate; as the salt concentration is increased, a parallel folding pathway emerges involving the less stable hairpin as an alternate intermediate. Notably, the flux between the pathways is modulated by the ionic strength. Our findings support the principle that the order of PK structure formation is determined by the relative stabilities of the hairpins, which can be altered by sequence variations or salt concentrations. The experimental results of salt effects on the partitioning between the two folding pathways are in remarkable agreement with simulations that were performed with no adjustable parameters. Our study not only unambiguously demonstrates that VPK folds by parallel pathways but also showcases the power of combining experiments and simulations for a more enriched description of RNA self-assembly.

Attribute based specification, comparison and selection of feed stock for anaerobic digestion using MADM approach.

Organic wastes are common in nature and generated at different sources which need to be treated before disposing into the environment. Anaerobic digestion (AD) process is a primary technique used for digestion and reduction of the ill effects of disposing the organic waste. Selection of appropriate feed stock for anaerobic digestion among the available options is a primary concern and the process efficiency and stability largely depend on this. The present paper describes a methodology for evaluation, comparison, ranking and optimum selection of a feed stock for anaerobic digestion. A 30 attribute coding scheme is proposed to evaluate the existing alternatives for feed stock of anaerobic digester. A three stage procedure which includes the elimination search is proposed to evaluate the available alternatives with the help of attributes quickly. Technique for order preference by similarity to ideal solution (TOPSIS) is a Multiple Attribute Decision Making (MADM) approach and graphical methods namely line graph and spider diagrams are used for optimum selection of feed stock among the available options. MATLAB code is written to execute the three stage procedure. The proposed methodology is explained through an illustrated example.