Impact of alternate wetting and drying irrigation and brown manuring on water use, weed control and yield of drum seeded rice

Direct-seeded rice (DSR) is a cost-effective and environmentally friendly method of crop establishment. Weed menaces in DSR considerably reduce the yield potential, which can be addressed by effective irrigation and weed management practices. Information on the impact of various water-saving irrigations and brown manure (BM) on water use, weed studies, and the yield of drum-sown rice is very limited. A field investigation was conducted to determine the effects of alternate wetting and drying irrigation (AWDI) methods (10 cm, 15 cm dropped from FWT and farmers practices) and BM (Sesbania at 15, 20 and 25 kg ha-1, Pretilachlor 0.45 kg ha-1 as PE fbBispyribac Na 25 g ha-1 as PoE + hand weeding (HW) on 45 DAS, HW at 20 and 45 DAS, and weedy check. The results revealed that AWDI at 15 cm depletion of FWT with HW on 20 and 45 DAS increased the water use efficiency (5.3 kg ha mm-1), water productivity (0.53 kg m-3), water saving percentage (35.83%), and reduced the water consumption (770 mm). Continuous submergence with HW at 20 and 45 DAS significantly increased grain (4.4 t ha-1) and straw yield (6.5 t ha-1). At the same time, it reduced the grasses (53.3 and 58.4%) and sedges (76 and 75%), density and dry weight, respectively, over AWDI at 10 cm dropped from FWT. Thus, irrigation at 10 cm below FWT with sesbania BM at 20 kg ha-1 could be recommended for higher productivity of drum-sown rice under sodic soil conditions

Sacrificial photolysis of water on TiO2 fine powders prepared by the hydrothermal method

The often discussed role of surface hydroxylation of TiO2 particles as an essential characterestics for their photocatalytic activity can be verified by preparing TiO2 powders by hydrothermal method since hydroxylated surface layers will be better retained on these particles formed in superheated water. Thus, fine powders of TiO2 (rutile) with high degree of crystallinity are formed from titanium oxychloride in the mixed solvent of water and 2-propanol at 160–230°C and 20–120 atm. The anatase phase is produced from the same medium when sulfate ion impurity is present, with Image . TiO2 powders are washed free of anions and 2-propanol by ultrafiltration and are Pt mounted by a photochemical method. Aqueous suspensions of both forms of TiO2 neither as such nor after Pt-loading, do not produce H2 on band gap illumination whereas, H2 is generated in presence of hole scavengers such as EDTA, TEOA, sulfite or hypophosphite. The effects of hole scavenger concentration, Pt : TiO2 ratio, particulate suspension density and the nature of hole scavengers on H2 production are presented. Platinised rutile powders are equally active as anatase in sacrificial systems

Photocatalytic activity of tin-substituted TiO2 in visible light

Ultrafine powders of (Ti1-xSnx)O2, 0<x≤1, prepared by the hydrothermal method under pressure, are pale-yellow in color. They show photocatalytic activity (after platinization) in the visible light region (420-550 nm) for H2 production from aqueous solutions containing sacrificial donors such as hypophosphite. The spectral sensitization is shown to be due to peroxotitanium species present in the lattice

The role of trap-centres on SrTiO3SrTiO_3 fine particles during water photolysis

$SrTiO_3$ fine powders prepared by different routes vary considerably by way of type and concentration of defect centres, as revealed by EPR investigations. The predominant electron-centres are $Ti^{3+}-V_O$ and V^1\hspace{1mm} _{Sr}, whereas the hole-centres correspond to O− adjacent to strontium vacancies. $SrTiO_3$ particles suspended in dilute acids under low intensity illumination show the presence of OH.s radicals. During water photolysis under band gap irradiation, the hole-centres on $SrTiO_3$ participate in the charge transfer to $OH^−$or other hole-scavenging species such as EDTA, $H_2PO_2^−$ or TEOA. Details of $H_2$ evolution kinetics of sacrificial photolysis system involving $H_2PO_2^−$ and $Pt/SrTiO_3$ are given. Reactivity of hole-centres on $SrTiO_3$ is higher than those on $TiO_2$, which accounts for $O_2$ evolution in photocatalyzed water-splitting in the case of $SrTiO_3$

Ultrafine powders of SrTiO3 from the hydrothermal preparation and their catalytic activity in the photolysis of water

Ultrafine powders of SrTiO3 are prepared at 100–150°C by the hydrothermal method, starting from TiO2·xH2O gel and Sr(OH)2 and H2O-isopropanol mixed solvent as the medium, The X-ray diffractograms of the powder show line broadening. The minimum crystallite size obtained ranges from 5 to 20nm with 20% H2O-80% C3H7OH as the reaction medium, as estimated from X-ray half-peak widths and TEM studies. The electron diffraction results indicate high concentration of lattice defects in these crystallites. The optical spectra of the particle suspensions in water show that the absorption around the band gap is considerably broadened, together with the appearance of maxima in the far ultraviolet. Aqueous suspensions of SrTiO3 powders, as such, do not produce H2 or O2 on UV irradiation. After coating with rhodium, H2 and O2 are evolved on illumination. However, the turn over number of O2 is lower than the stoichiometrically expected values from the corresponding values of H2. No correlation of the photocatalytic activity with surface area is observed. The activity of Rh-SrTiO3 slowly deteriorates with extended period of irradiation

Sacrificial water photocleavage using Nb-doped TiO2TiO_2 fine particles under band gap irradiation

Ultrafine powders of $TiO_2$ doped with $Nb^{5+}$ up to 10 mol% are produced by the hydrothermal procedure at 150–180 C and 1–4 MPa. Aqueous suspensions of these powders do not produce $H_2$ on band gap irradiation, even after Pt-loading. $H_2$ is evolved only in presence of a hole scavenger, such as EDTA. $H_2$ -evolution capacity of $TiO_2$ is enhanced up to $\sim$ 0.3 mol% Nb and reverses the trend at higher Nb-concentrations. $H_2$ -yield is not related to anatase/rutile phase content. The decrease in $H_2$ production with $TiO_2$:Nb is due to the Schottky type of defect centres with donor character, that are charge-compensatively formed in $TiO_2$ and act as electron traps. The accumulation of electrons in Nb-doped $TiO_2$ is supported by the electron paramagnetic resonance and the current potential measurements under illumination of the slurry electrode cells

Photocatalysis on Fine Powders of Perovskite Oxides

Fine powders of semiconductor oxides have been widely used as photocatalysts for many reactions. Among the various photocatalytic reactions, water splitting has been given much importance, since it is a promising chemical route for solar energy conversion. Perovskite oxides, in particular SrTiO, have been commonly used as photocatalysts because some of them can decompose H,O into H, and 0, without an external bias potential (1). In turn, this is because the conduction band (CB) edges of some of the perovskite oxides are more negative than the H+/H, energy level. Since the catalytic activity is related to the surface properties of the solids, fine powders rather than single crystals are used. Photocatalysis on fine powers can be conveniently discussed in three parts, viz. preparation, characterization and their catalytic activity. Presently, photo-decomposition of water using SrTiO, fine powders is discussed in greater detail, although other photocatalytic reactions on various perovskite oxides are also briefly dealt with

Characteristics of the surface states produced on titanate photoanodes by mechanical polishing

Investigations using repetitive triangular potential sweeps and X-ray photo electron spectroscopy reveal that stable, surface-bound peroxotitanium species are produced without illumination on mechanically polished n-type $SrTiO_3, SrTi_3O7, BaTiO_3, BaTi_4O_9 and TiO_2$ polycrystalline photoelectrodes in alkaline media, under anodic polarization. Formation of peroxotitanium species is related to the chemical reactivity of the surface regions that incorporate the mechanically-induced crystalline defects, according to the scheme: $2OH_s^- = (O_2^{2-})_s + 2H^+ + 2e^-$. Bulk flaws present the mechanically damaged surface region allow a quasi-isoenergetic transfer of electrons from the conduction band at the bulk to empty surface states (peroxo species). At much more anodic potential [$V_{appl}$ $^>_\sim$ 0.45 V (SCE)], the Fermi level is pushed below the surface states and the electrons are transferred from ss to the CB via bulk flaws, leading to the underpotential evolution of oxygen: $(O_2^{2-})_s = O_2 + 2e^-$

Bulk versus surface state contributions to the efficiency of perovskite titanate photoanodes

Attempts have been made to enhance the photon efficiency of perovskite titanate electrodes during band gap illumination by increasing the bulk dielectric constant with the substitution of suitable isovalent ions in the lattice so that the Curie point 1s shifted to room temperature and by decreasing the $N_n$ values with controlled chemical reduction.The photoresponse showed only marginal improvements with these changes in the bulk characteristics. In comparison, the efficiency increased considerably when the electrode surfaces are treated by exposing to dilute acids. particularly $HNO_3+HF$, for extended periods of time. This is accompanied by the changes in $V_{on}$ to cathodic direction, red shift in the spectral dependence of photoresponse and marginal decrease of $N_n$ in the space charge layer. X-ray photoelectron spectra show that the treated electrode surfaces are not uniform with respect to oxygen/titanium ratios, hydroxyls and fluoride incorporated. The enhanced photon efficiency arises from the combined effect of eliminatmg the undesirable electron recombination centres in the space charge layer and the presence of heterogeneous surface regions leading to non-uniform potential distribution near the electrode surface. The results also point to the limitations of applying Schottky barrier model for semiconductor/electrolyte interface with higher concentrations of surface states