Muhammad Ali Ehsan

Performance of cobalt titanate towards H2O2 based catalytic oxidation of lignin model compound

Mixed metal cobalt titanium oxide (CoTiO3) prepared by solution phase method has been evaluated for the liquid phase catalytic oxidation of vainlly alcohol to vanillin using H2O2 as an oxygen source. The morphology, phase composition and crystal structure of the freshly prepared and reused CoTiO3 catalyst was studied by SEM, EDX, XRD, XPS and Raman spectroscopy. Vanillyl alcohol conversion was influenced by various experimental conditions such as reaction time, temperature, molar ratio of reactants, catalyst loading, nature of solvent and reaction medium. The design a heterobimetallic oxide catalyst which can efficiently perform the high conversion and selective oxidation of vanillyl alcohol into fine chemicals, such as vanillin and vanillic acid. It has been found that during the 5 h reaction in NaOH, the CoTiO3 exhibits remarkable conversion of 99% and excellent selectivity of 99.8% to vanillin was achieved in acetic acid and isopropanol solvents, respectively. The oxidation reaction mechanism over the catalyst was postulated based on the observation product from the HPLC analysis. CoTiO3 catalyst can retain its performance without significant change in the catalytic activity after four consecutive cycles.

Hexagonal structured Zn(1−x)CdxO solid solution thin films: synthesis, characterization and applications in photoelectrochemical water splitting

Hexagonal nanostructured zinc–cadmium oxide [Zn(1−x)CdxO where x = 0.08, 0.15, and 0.17] solid solution thin films were deposited on FTO coated glass substrates from a common solution of zinc acetate and a newly developed polymeric cadmium precursor by an aerosol-assisted chemical vapour deposition (AACVD) technique. The polymeric cadmium precursor [Cd3(TFA)4(OAc)2(THF)4]n (1) was synthesized by the reaction of cadmium(II)acetate dihydrate with triflouroacetic acid in THF solution and characterized by melting point, microanalysis, FTIR, 1H-NMR, thermogravimetry (TG/DTG) and single crystal X-ray analysis. The deposited thin films were characterized by powder XRD, SEM, EDX and UV-visible spectrophotometry, and tested for photoelectrochemical (PEC) water splitting to hydrogen and oxygen. The effect of various thin film deposition parameters such as solvent type, temperature and electrolyte concentration on PEC properties has been investigated. The SEM analysis illustrated that the morphology of the films changes significantly with the change of the solvent. The films deposited from THF solution have a needle-like appearance scattered vertically on the FTO-coated glass substrate. An optical band gap of 2.40 eV has been estimated by UV-visible spectrophotometry. The current–voltage characterization proved that the nanocrystalline hexagonal structured Zn0.83Cd0.17O electrodes exhibit an n-type semiconducting behaviour and the photocurrent was found to be strongly dependent on the deposition solvent, deposition temperature and electrolyte concentration. The maximum photocurrent density of 0.23 mA cm−2 at 0.55 V vs. Ag/AgCl/3 M KCl (∼1.23 V vs. RHE) was obtained for the Zn0.83Cd0.17O photoelectrode deposited at 500 °C for 45 min from 0.5 M solution of (1) and Zn(CH3COO)2·2H2O in THF.

Core–Shell Vanadium Modified Titania@β-In2S3 Hybrid Nanorod Arrays for Superior Interface Stability and Photochemical Activity

Core-shell rutile TiO2@β-In2S3 and modified V-TiO2@β-In2S3 were synthesized to develop bilayer systems to uphold charge transport via an effective and stable interface. Morphological studies revealed that β-In2S3 was deposited homogeneously on V-TiO2 as compared to unmodified TiO2 nanorod arrays. X-ray photoelectron spectroscopy (XPS) and electron energy loss spectrometry studies verified the presence of various oxidation states of vanadium in rutile TiO2 and the vanadium surface was utilized for broadening the charge collection centers in host substrate layer and hole quencher window. Subsequently, X-ray diffraction, high-resolution transmission electron microscopy, and Raman spectra confirmed the rutile phases of TiO2 and modified V-TiO2 along with the phases of crystalline β-In2S3. XPS valence band study explored the interaction of valence band quazi Fermi levels of β-In2S3 with the conduction band quazi Fermi levels of modified V-TiO2 for enhanced charge collection at the interface. Photoelectrochemical studies show that the photocurrent density of V-TiO2@β-In2S3 is 1.42 mA/cm(2) (1.5AM illumination). Also, the frequency window for TiO2 was broadened by the vanadium modification in rutile TiO2 nanorod arrays, and the lifetime of the charge carrier and stability of the interface in V-TiO2@β-In2S3 were enhanced compared to the unmodified TiO2@β-In2S3. These findings highlight the significance of modifications in host substrates and interfaces, which have profound implications on interphase stability, photocatalysis and solar-fuel-based devices.

Nitrite ion sensing properties of ZnTiO3–TiO2 composite thin films deposited from a zinc–titanium molecular complex

A titanium based heterobimetallic molecular precursor, [Zn2Ti4(μ-O)6(TFA)8(THF)6]·THF (1) (where TFA = trifluoroacetato; THF = tetrahydrofuran), has been designed and scrutinised for its various physicochemical properties by melting point analysis, microanalysis, Fourier transform infra-red spectroscopy, proton nuclear magnetic resonance spectroscopy, thermogravimetry and single crystal X-ray structural analysis. ZnTiO3–TiO2 composite thin films were grown on a fluorine doped tin oxide (FTO) coated conducting glass substrate at 550 °C from three different solutions of (1) viz. methanol, THF and acetonitrile, by the aerosol-assisted chemical vapour deposition technique. The phase identification, chemical composition and microstructure of the fabricated thin films that were probed by powder X-ray diffraction, Raman spectroscopy, energy dispersive X-ray analysis and scanning electron microscopy revealed the formation of a 1 : 1 ratio of ZnTiO3 : TiO2 composite microspheres of diverse designs and textures depending on the type of deposition solvent used. The direct band gap energy of 3.1 eV was estimated by UV-visible spectrophotometry of the ZnTiO3–TiO2 film fabricated from methanol solution and the film electrode was further tested as an electrochemical sensor for the detection of nitrite ions.

Electrochemical sensing of nitrite using a copper–titanium oxide composite derived from a hexanuclear complex

A hexanuclear copper–titanium complex [Cu2Ti4(O)2(OH)4(TFA)8(THF)6]·THF (1) (where TFA = trifluoroacetato, THF = tetrahydrofuran) has been identified for the treatment of copper(II) acetate with titanium(IV) isopropoxide and trifluoroacetatic acid in THF. The physicochemical properties of complex (1) have been inspected by melting point analysis, microanalysis, attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetry and single crystal X-ray analysis. The “single source” potential of complex (1) has been explored by a solution based aerosol assisted chemical vapor deposition method to fabricate CuO–2TiO2 composite oxide thin films on a fluorinated tin oxide (FTO) conducting glass substrate at 550 °C in ambient air. Thin film characterization such as X-ray powder diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy, energy dispersive X-ray and scanning electron microscopic analyses confirm the evolution of crystalline CuO: a 2TiO2 composite with spherical morphology, with clear grain boundaries and in high purity. Further, the well-characterized film electrode was investigated for electrochemical detection of nitrite ions (NO2−). The fabricated CuO–2TiO2 electrode showed a peak at +1.0 V due to the oxidation of NO2− ions. The limit of detection (LoD) was found to be 0.0166 μM, with the linear range of 10 to 200 μM. Moreover, this present sensor is more selective towards NO2− ions and it did not show any response to other interfering species. This CuO–2TiO2 electrode is a potential candidate for the selective and sensitive detection of toxic NO2− ions towards monitoring the NO2− ion levels in natural water sources for environmental remediation applications.

Bis(O-n-butyl dithio­carbonato-κ2 S,S′)bis­(pyridine-κN)manganese(II)

The structure of the title manganese complex, [Mn(C5H9OS2)2(C5H5N)2] or [Mn(S2CO-n-Bu)2(C5H5N)2], consists of discrete monomeric entities with Mn2+ ions located on centres of inversion. The metal atom is coordinated by a six-coordinate trans-N2S4 donor set with the pyridyl N atoms located in the apical positions. The observed slight deviations from octahedral geometry are caused by the bite angle of the bidentate κ2-S2CO-n-Bu ligands [69.48 (1)°]. The O(CH2)3(CH3) chains of the O-n-butyl dithiocarbonate units are disordered over two sets of sites with an occupancy ratio of 0.589 (2):0.411 (2).

Fabrication of CuO–1.5ZrO2 composite thin film, from heteronuclear molecular complex and its electrocatalytic activity towards methanol oxidation

A heteronuclear coordination complex [Cu4Zr6(μ-O)8(dmap)4(OAc)12]·H2O (1), where dmap = N,N-dimethylaminopropanolato and −OAc = acetato, has been isolated in pure form by the chemical interaction of Zr(dmap)4 with Cu(OAc)2·H2O in THF. Complex (1) has been examined by melting point, elemental analysis, FT-IR spectroscopy and single crystal X-ray diffraction. The thermal decomposition behavior of the complex has been explored by thermogravimetric, derivative thermogravimetric and differential scanning calorimetric analyses which reveal that complete conversion of (1) into 1 : 1.5 composite oxides, CuO : ZrO2, treated at 500 °C. The ability of complex (1) to act as a single-source precursor for the formation of advanced composite oxides thin film has been investigated by aerosol assisted chemical vapor deposition at 550 °C in air ambient. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) analyses of the developed thin films suggest the formation of good quality crystalline microspherical-shaped CuO–1.5ZrO2 composite oxide with high purity. The electrocatalytic activity of CuO–1.5ZrO2 composite oxide film was studied toward methanol oxidation in an alkaline medium and it showed high oxidation peak current of 14 μA during a forward scan which is ∼3.5-fold higher than the bare Pt electrode. The ease and low cost fabrication and high electrocatalytic activity of composite oxide film could make it potential candidate for direct methanol fuel cells application.

Vysotskite structured photoactive palladium sulphide thin films from dithiocarbamate derivatives

A series of palladium(II) dithiocarbamate complexes [Pd(S2CNRR′)2]·n(py) [where py = pyridine; RR′ = Bz, n = 1 (1); Cy, n = 1 (2); nHex, n = 0 (3) and MeCy, n = 0 (4)] have been synthesized and characterized using various physicochemical techniques and their single crystal structures have been established. The decomposition modes and potential of the complexes as single source precursors (SSPs) for the development of palladium sulphide (PdS) thin films were investigated by thermogravimetric and derivative thermogravimetric (TGA/DTG) analyses. The PdS thin films were deposited on FTO conducting glass substrates at 400, 450 and 500 °C by the aerosol-assisted chemical vapour deposition (AACVD) technique and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) reveal that the deposit has a tetragonal structure with a 1 : 1 ratio of Pd : S. The shape and size of PdS crystallites and the texture of films depend on the deposition temperatures and the precursor type used. The direct band gap energy of 1.56 eV was estimated from UV-Vis spectroscopy of the PdS films fabricated from precursor (2) at 450 °C. The photoelectrochemical (PEC) properties of PdS films were studied by recording the current–voltage plots under alternating dark and illumination conditions. To the best of our knowledge, this is the first demonstration of PEC studies of photoactive PdS thin films fabricated using the AACVD technique using palladium(II) dithiocarbamate complexes as precursors.

Single step aerosol assisted chemical vapor deposition of p–n Sn(II) oxide–Ti(IV) oxide nanocomposite thin film electrodes for investigation of photoelectrochemical properties

A homogeneous 1 : 1 solution of tetraisopropoxytitanium(IV) and [Sn(OAc)(dmae)]2 precursors in toluene was used at 450 °C, under argon, to deposit p–n-type tin(II) oxide–titanium(IV) oxide nanocomposite thin film electrodes by a single step aerosol assisted chemical vapor deposition (AACVD) technique. Field emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), Raman scattering, energy-dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectrophotometry were conducted to characterize the thin film electrodes. The deposited thin film electrodes were tested for their applications in water photolysis. A comparison of the photoelectrochemical properties of the deposited SnO–TiO2 composite electrodes with those of pristine TiO2 and SnO electrodes fabricated from tetraisopropoxytitanium(IV) and [Sn(OAc)(dmae)]2, respectively, indicates a higher photocatalytic activity as compared to pristine TiO2. This is possibly due to the incorporation of p-type SnO, which effectively promoted the separation of photogenerated charge carriers to rectify electron transfer from SnO to TiO2, leading to the separation of electron–hole pairs. The combined synergistic effect of p-type SnO and n-type TiO2, flower-like morphology and augmented ability to absorb solar light produced a significantly enhanced photocurrent of ∼4.3 mA cm−2 at 0.7 V vs. Ag/AgCl electrode. No obvious photocurrent decay was noted for prolonged stability measurements of up to 60 min under one sun illumination of 100 mW cm−2. With such a facile synthetic strategy and enhanced performance profile, the resulting material provides inspiration for producing new p–n-type composite photoanodes for better PEC performance using similar strategies.