High-Performance Broadband Self-Driven Photodetector Based on MoS2/Cs2CuBr4 Heterojunction.

Few-layer transition metal dichalcogenides and perovskites are both promising materials in high-performance optoelectronic devices. Here, we developed a self-driven photodetector by creating a heterojunction between few-layer MoS2 and lead-free perovskite Cs2CuBr4. The detector shows a unique property of very high sensitivity in a broad spectral range of 400 to 800 nm with response speed in a millisecond order. Current-voltage characteristics of the heterojunction device show rectifying behavior, in contrast to the ohmic behavior of the MoS2-based device. The rectifying behavior is attributed to the type II band alignment of the MoS2/Cs2CuBr4 heterojunction. The device shows a broadband (400 to 800 nm) photodetection with very high responsivity reaching up to 2.8 × 104 A/W and detectivity of 1.6 × 1011 Jones at a bias voltage of 3 V. The detector can also operate in self-bias mode with sufficient response. The photocurrent, photoresponsivity, detectivity, and external quantum efficiency of the device are found to be dependent on the illumination power density. The response time of the device is found to be ∼32 and ∼79 ms during the rise and fall of the photocurrent. The work proposes a MoS2/Cs2CuBr4 heterostructure to be a promising candidate for cost-effective, high-performance photodetector.

Studying Molecular Rearrangement of P1 Dye at a Passivating Alumina Surface Using Vibrational Sum-Frequency Generation Spectroscopy: Effect of Atomic-Level Roughness.

The effect of roughness and thickness of alumina layers, mimicking the passivation layer commonly used in dye-sensitized photoelectrodes, on the molecular adsorption of P1 dye, 4-(bi(4-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl]-aminobenzoic acid) has been studied using surface-sensitive vibrational sum frequency generation(VSFG) spectroscopy. The VSFG spectra reveal the formation of poorly ordered dye layers on relatively rough surfaces where XPS measures a higher dye loading. Furthermore, these poorly ordered dye molecules are responsible for the generation of trapped electronic states as probed by successive photoluminescence (PL) measurements. Surface sensitive VSFG spectroscopy in combination with XPS and PL measurements provide complementary spectral information on ordering of the adsorbed dyes, their density on the surface and electronic states of the adsorbed monolayer which are prerequisite for improving our understanding of molecularly functionalized photoelectrodes and their further development.

2-Propanol interacting with Co3O4(001): A combined vSFS and AIMD study.

The interaction of 2-propanol with Co3O4(001) was studied by vibrational sum frequency spectroscopy and ab initio molecular dynamics simulations of 2-propanol dissolved in a water film to gain an insight, at the molecular level, into the pathways of catalytic oxidation. The experimental study has been performed under near ambient conditions, where the presence of water vapor is unavoidable, resulting in a water film on the sample and, thereby, allowing us to mimic the solution-water interface. Both experiment and theory conclude that 2-propanol adsorbs molecularly. The lack of dissociation is attributed to the adsorption geometry of 2-propanol in which the O-H bond does not point toward the surface. Furthermore, the copresent water not only competitively adsorbs on the surface but also inhibits 2-propanol deprotonation. The calculations reveal that the presence of water deactivates the lattice oxygen, thereby reducing the surface activity. This finding sheds light on the multifaceted role of water at the interface for the electrochemical oxidation of 2-propanol in aqueous solution as recently reported [Falk et al., ChemCatChem 13, 2942-2951 (2021)]. At higher temperatures, 2-propanol remains molecularly adsorbed on Co3O4(001) until it desorbs with increasing surface temperature.

Anti-organic fouling and anti-biofouling poly(piperazineamide) thin film nanocomposite membranes for low pressure removal of heavy metal ions.

Propensity towards anti-organic fouling, anti-biofouling property and low rejection of multivalent cation (monovalent counter ion) restricts the application of the state-of-art poly(piperazineamide) [poly(PIP)] thin film composite (TFC) nanofiltration (NF) membrane for the treatment of water containing toxic heavy metal ions, organic fouling agents and microbes. Herein, we report the preparation of thin film nanocomposite (TFNC) NF membranes with improved heavy metal ions rejection efficacy, anti-biofouling property, and anti-organic fouling properties compared to that of poly(PIP) TFC NF membrane. The TFNC NF membranes were prepared by the interfacial polymerization (IP) between PIP and trimesoyl chloride followed by post-treatment with polyethyleneimine (PEI) or PEI-polyethylene glycol conjugate and then immobilization of Ag NP. The IP was conducted on a polyethersulfone/poly(methyl methacrylate)-co-poly(vinyl pyrollidone)/silver nanoparticle (Ag NP) blend ultrafiltration membrane support. The TFNC membranes exhibited >99% rejection of Pb2+, 91-97% rejection of Cd2+, 90-96% rejection of Co2+ and 95-99% rejection of Cu2+ with permeate flux ∼40Lm-2h-1 at applied pressure 0.5MPa. The improved heavy metal ions rejection efficacy of the modified NF membranes is attributed to the development of positive surface charge as well as lowering of surface pore size compared to that of unmodified poly(PIP) TFC NF membrane.

Ab initio multiple spawning dynamics study of dimethylnitramine and dimethylnitramine-Fe complex to model their ultrafast nonadiabatic chemistry.

Conical intersections are now firmly established to be the key features in the excited electronic state processes of polyatomic energetic molecules. In the present work, we have explored conical intersection-mediated nonadiabatic chemical dynamics of a simple analogue nitramine molecule, dimethylnitramine (DMNA, containing one N-NO2 energetic group), and its complex with an iron atom (DMNA-Fe). For this task, we have used the ab initio multiple spawning (AIMS) dynamics simulation at the state averaged-complete active space self-consistent field(8,5)/6-31G(d) level of theory. We have found that DMNA relaxes back to the ground (S0) state following electronic excitation to the S1 excited state [which is an (n,π*) excited state] with a time constant of approximately 40 fs. This AIMS result is in very good agreement with the previous surface hopping-result and femtosecond laser spectroscopy result. DMNA does not dissociate during this fast internal conversion from the S1 to the S0 state. DMNA-Fe also undergoes extremely fast relaxation from the upper S1 state to the S0 state; however, this relaxation pathway is dissociative in nature. DMNA-Fe undergoes initial Fe-O, N-O, and N-N bond dissociations during relaxation from the upper S1 state to the ground S0 state through the respective conical intersection. The AIMS simulation reveals the branching ratio of these three channels as N-N:Fe-O:N-O = 6:3:1 (based on 100 independent simulations). Furthermore, the AIMS simulation reveals that the Fe-O bond dissociation channel exhibits the fastest (time constant 24 fs) relaxation, while the N-N bond dissociation pathway features the slowest (time constant 128 fs) relaxation. An intermediate time constant (30 fs) is found for the N-O bond dissociation channel. This is the first nonadiabatic chemical dynamics study of metal-contained energetic molecules through conical intersections.

Multifunctionalization of Poly(vinylidene fluoride)/Reactive Copolymer Blend Membranes for Broad Spectrum Applications.

Simultaneous immobilization and cross-linking of antifouling/low toxic polymers, e.g., poly(ethylenimine) (PEI), dextran (Dex), agarose (Agr), poly(ethylene glycol) (PEG), PEI-Dex, and PEI-PEG conjugates, and stimuli-responsive copolymers on a porous membrane surface in mild reaction conditions is desirable for the enhancement of hydrophilicity, antifouling character, cytocompatibility, and inducing stimuli-responsive behavior. Grafting to technique is required since the precursors of most of these macromolecules are not amenable to surface-initiated polymerization. In this work, we report a versatile process for the simultaneous immobilization and cross-linking of a library of macromolecules on and into the blend membrane (PVDF-blend) of poly(vinylidene fluoride) and poly(methyl methacrylate)-co-poly(chloromethylstyrene). Sequential nucleophilic substitution reaction between activated halide moieties of the copolymer and amine groups of different macromolecules readily provided series of modified membranes. These membranes exhibited antifouling property superior to that of the unmodified membrane. The effectiveness of this technique has been demonstrated by the immobilization of pH or both pH- and temperature-responsive copolymer on PVDF-blend membrane for responsive separation of poly(ethylene oxide) and bovine serum albumin. Silver nanoparticles were also anchored on the select modified membranes surfaces for the enhancement of antibiofouling property. Our approach is useful to obtain verities of functional membranes and selection of membrane for a particular application.

Degradable/cytocompatible and pH responsive amphiphilic conetwork gels based on agarose-graft copolymers and polycaprolactone.

Amphiphilic conetwork (APCN) gels have emerged as an important class of biomaterials due to their diverse applications. APCN gels based on biocompatible/biodegradable polymers are useful for controlled release and tissue engineering applications. Herein, we report a facile synthesis of APCN gel films by click type sequential nucleophilic substitution reaction between pendent tertiary amine groups of agarose-g-poly(methyl methacrylate)-b(co)-poly(2-dimethylamino)ethyl methacrylate [Agr-g-PMMA-b(co)-PDMA] copolymers and activated benzyl chloride groups of polychloromethyl styrene or benzyl methyl chloride terminated polycaprolactone. A linear triblock copolymer (PDMA-b-PMMA-b-PDMA) containing a central PMMA block and end PDMA blocks was also employed for the synthesis of APCN gels for comparison purposes. These APCN gels exhibit co-continuous nanophase morphology, pH responsive water swelling and pH triggered release of hydrophobic and hydrophilic drugs. These gels are biodegradable/cytocompatible as confirmed by MTT assay and hemolysis experiment. The degraded species undergo micellization in aqueous environment and display a low critical micelle concentration. Milled APCN gel particles are injectable through a hypodermic syringe. This synthesis approach is extremely useful for the preparation of a library of APCN gels of diverse architectures and compositions for biomedical applications.

Microbial synthesis of polyhydroxyalkanoate using seaweed-derived crude levulinic acid as co-nutrient.

Production of polyhydroxyalkanoates (PHAs) from Jatropha biodiesel residues, namely crude glycerol and oil cake hydrolysate, has been reported previously. Halomonas hydrothermalis (MTCC accession no. 5445; NCBI Genbank accession no. GU938192), a wild marine strain, was used in the bio-synthesis. The present study was initiated to vary the properties of the polymer. Seaweed-derived crude levulinic acid (SDCLA), containing formic acid, residual sugars and dissolved minerals additionally, was proposed as co-feed along with the biodiesel residues. Experiments were conducted at 100mL scale in batch process. Whereas the PHA yield was only 0.40 ± 0.01 g when only biodiesel residues were employed, it rose to 1.07 ± 0.02 g in presence of 0.35% (w/v) of SDCLA. The corresponding carbon utilisation efficiencies were 29.3% and 57.5%, respectively. 3-Hydroxy valerate incorporation in the PHA was pronounced in presence of SDCLA, with associated changes in polymer properties. The microbial synthesis fared poorly when SDCLA was substituted with pure levulinic acid. Thus, Halomonas hydrothermalis had a poor response to levulinic acid, as such, and other constituents present in SDCLA appear to have played a vital role in bacterial cell division and accumulation of PHA. Biodegradability tests in moist soil were also conducted as part of the study. Marine microalgal cultivation for biodiesel and seaweed cultivation for fuels may help generate biodiesel residues and crude levulinic acid in proximity, which would open up the possibility of large scale PHA manufacture in efficient and practical manner in the future through the methodology of the present study.