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A systematic study on the preparation of SnO2 nanoparticles using a simple sol-gel technique has been conducted by varying reaction parameters such as concentration of ammonia, ammonia feed rate and reaction temperature. The tin oxide obtained was characterized by using FTIR, BET, XRD and TEM. Particles size was obtained in the range of 4 to 5 6 nm and the surface area was found to be between 76 to 114 m(2) g(-1) depending on the reaction parameters. Meanwhile, the catalytic activity of SnO2 was first time investigated for the hydrogenation reaction of styrene using ethanol as the solvent at 70 degrees C and 1 atmospheric pressure It is found that SnO2 acts as a good catalyst in this hydrogenation process The product conversions in the presence of catalysts prepared at different conditions were between 37 to 72%.

Tin oxide nanoplates and nanoballs were fabricated using a cationic surfactant of cetyltrimethylammonium bromide (CTABr) as an organic supramolecular template and tin(IV) chloride as an inorganic precursor via the hydrothermal and conventional heating methods. Urea, which decomposes to ammonium and hydroxide ions during hydrolysis, was used as the source of slow homogeneous precipitation of Sn4+ with OH- to control the particle size. The influence of different reaction parameters (time, temperature, and ratio of Sn4+ to CTABr) on particle sizes, particle distribution, and morphology was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. XRD data showed that the size of the SnO2 nanoparticles decreased with increasing reaction time using the conventional heating method, while no significant change was observed with the hydrothermal method. Nanoplates with average sizes of 9.36 nm and nanoballs up to 4.51 nm were prepared using different ratios of Sn+4 to CTABr at different temperatures and reaction times by the hydrothermal and conventional heating methods, respectively. Elimination of surfactant from tin-surfactant composites by calcination yielded a porous tin oxide nanostructure.

Department of Chemistry, University of Karachi, Karachi-75270, Pakistan E-mail: abida2020@yahoo.com Manuscript received 15 March 2004, revised 28 July 2004, accepted 23 August 2004 The kinetics of the redox reaction between diphenylbenzidine (DPB) and thiosulfate was investigated in the range pH 2.0 to 4.5. Order of reaction with respect to thiosulfate, diphcnylbenzidine and H+ was found to be one. The following rate law is recommended : Rate= k1 [DPB] [S2O2-3] + k2 K {DPB [H+]} [S2O2-3] where k1, k2 are the rate constants for the reaction [DPB] + S2O2-3→ [S4O2-6] + Product having the values of k1 = 5.557 x 103 dm3 mol-1 s-1 and k2 = 5.827 x 108 dm3 mol-1 s-1 K is the protonation constant of DPB having value of 476 dm3 mol-1.

In the title compound, C20H18ClN5S, the toluene and triazole rings are oriented almost perpendicular to each other, making a dihedral angle of 89.97 (9)°, whereas the dihedral angle between cholorophenyl and pyrazole rings is 54.57 (11)°. In the crystal, pairs of N—H...N hydrogen bonds link the molecules into inversion dimers. Weaker C—H...S and C—H...Cl interactions are also present.

Department of Chemistry University of Karachi Karachi 75270, Pakistan E mail:akhyar100@yahoo corn Manuscript received 27 November 2001 reared 3 July 2002 accepted 14 November 2002 13isacetvlacctonatodiaquomanganese(III) complex has been prepared in perchloric acid medium Kinetic order of the reduction of this complex pith thiosultate is established The reaction follows first order kinetics in complex, tractional order in both thiosulfate and [H+] The redox mechanism has been explained and the rate law derived Activation parameters are computed and an outer-sphere mechanism is suggested for the reaction.

Al-doped ZnO (AZO) thin films were potentiostatically deposited on indium tin oxide substrates. The influence of the doping level of the ZnO:Al films was investigated. The results of the X-ray diffraction and scanning electron microscopy analysis revealed that the structural properties of the AZO films were found polycrystalline with a hexagonal wurtzite-type structure along the (002) plane. The grain size of the AZO films was observed as approximately 3 μm in the film doping with 4 mol% ZnO:Al concentration. The thin films also exhibited an optical transmittance as high as 90 % in the wavelength range of 100–1,000 nm. The optical band gap increased from 3.33 to 3.45 eV. Based on the Hall studies, the lowest resistivity (4.78 × 10−3 Ω cm) was observed in the film doping with 3 mol% ZnO:Al concentration. The sheet resistant, carrier concentration and Hall mobility values were found as 10.78 Ω/ square, 9.03 × 1018 cm−3 and 22.01 cm2/v s, respectively, which showed improvements in the properties of AZO thin films. The ZnO:Al thin films were used as a buffer layer in thin-film solar cells with the structure of soda-lime glass/Mo/Cu2ZnSnS4/ZnS/ZnO/Al grid. The best solar cell efficiency was 2.3 % with V OC of 0.430 V, J SC of 8.24 mA cm−2 and FF of 68.1 %.

The kinetics of the reaction between vitamin C ( l -ascorbic acid) and ferric chloride hexahydrate was investigated in acidic medium at pH 3 spectrophotometrically. The order of the reaction was established by applying different methods, such as initial rate method, integration method and half-life method. The results obtained from each method were correlated with each other and consistency in all methods was observed. The order of the reaction with respect to each reactant was found first and the overall second order was recommended for the reaction.