Complete desalination of seawater using a novel polyvinylidene fluoride/zeolite membrane

Water scarcity arises rapidly with increasing human population, urbanization and industrialization. Therefore, water production from natural sources using efficient and environmental friendly technologies is gaining attention. Pervaporative desalination is a promising technology based upon membrane filtration. Here, we fabricated and tested a novel hybrid-composite membrane: polyvinylidene fluoride (PVDF)/polyvinyl pyrrolidone/(PVP)/3A zeolite. Desalination performance was evaluated in terms of flux, salt rejection, zeolite incorporation within the membrane and temperature. Results show that all membranes exhibited salt rejection higher than 99.5%. The highest flux of 2.5 kg m^?2 h^?1 and salt rejection of 99.9% were obtained using 10 wt% 3A incorporated PVDF/PVP membrane at 40 °C. The PVDF/PVP/3A zeolite membrane preserved its stability during 55-h desalination operating without performance decline.     

Environmental impact of CO<Subscript>2</Subscript>, Rn,Hg degassing from the rupture zones produced by Wenchuan <Emphasis Type="Italic">M</Emphasis><Subscript>s</Subscript> 8.0 earthquake in western Sichuan,China

The concentrations and flux of CO₂, ²²²Radon (Rn), and gaseous elemental mercury (Hg) in soil gas were investigated based on the field measurements in June 2010 at ten sites along the seismic rupture zones produced by the May 12, 2008, Wenchuan M _s 8.0 earthquake in order to assess the environmental impact of degassing of CO₂, Rn and Hg. Soil gas concentrations of 344 sampling points were obtained. Seventy measurements of CO₂, Rn and Hg flux by the static accumulation chamber method were performed. The results of risk assessment of CO₂, Rn and Hg concentration in soil gas showed that (1) the concentration of CO₂ in the epicenter of Wenchuan M _s 8.0 earthquake and north end of seismic ruptures had low risk of asphyxia; (2) the concentrations of Rn in the north segment of seismic ruptures had high levels of radon, Maximum was up to level 4, according to Chinese code (GB 50325-2001); (3) the average geoaccumulation index I _geo of soil Hg denoted the lack of soil contamination, and maximum values classified the soil gas as moderately to strongly polluted in the epicenter. The investigation of soil gas CO₂, Rn and Hg degassing rate indicated that (1) the CO₂ in soil gas was characterized by a mean \(\updelta^{13}C_{CO2}\) of ?20.4 ‰ and by a mean CO₂ flux of 88.1 g m^?2 day^?1, which were in the range of the typical values for biologic CO₂ degassing. The maximum of soil CO₂ flux reached values of 399 g m^?2 day^?1 in the epicenter; (2) the soil Rn had higher exhalation in the north segment of seismic ruptures, the maximum reached value of 1976 m Bq m^?2 s^?1; (3) the soil Hg flux was lower, ranging from ?2.5 to 18.7 n g m^?2 h^?1 and increased from south to north. The mean flux over the all profiles was 4.2 n g m^?2 h^?1. The total output of CO₂ and Hg degassing estimated along seismic ruptures for a survey area of 18.17 km² were approximately 0.57 Mt year^?1 and 688.19 g year^?1. It is recommended that land-use planners should incorporate soil gas and/or gas flux measurements in the environmental assessment of areas of possible risk. A survey of all houses along seismic ruptures is advised as structural measures to prevent the ingress of soil gases, including CO₂ and Rn, were needed in some houses.     

Assessment of methane from agricultural field during the entire paddy cropping seasons – a case study

A systematic effort was made to assess the emission of methane from paddy fields using closed chamber technique. Methane emission measurements were performed over a year during the Kharif (wet season), Rabi (dry season), and fallow periods. Various soil parameters like redox potential, organic carbon and ferrous ion were determined to evaluate their control on methane emissions. Diurnal measurement of the flux showed a minimum (0.44?mg?m^?2?h^?1) in the morning (8?a.m.), which increased gradually to a value of 1.16?mg?m^?2?h^?1 till the evening due to the rise in soil temperature. The seasonally integrated flux (E _SIF) for CH₄ was calculated. The E _SIF for methane during Kharif and Rabi crops were found to be 5.97?g?m^?2 and 2.59?g?m^?2, respectively. It was observed that the methane flux was maximum during flowering and fertilizer application stages for both paddy cropping seasons. The redox potential was low and the ferrous ion was higher during flowering and tiller stages. The methane emission was higher at E _AIF) was calculated for methane to make a budget estimate of methane emission from rice cultivated under rain fed drought prone water regime.     

Nanostructured semiconducting materials for efficient hydrogen generation

Massive production of hydrogen by water decomposition triggered by a solar light active photocatalyst is a major objective in chemistry and a promising avenue to overcome the global energy crisis. The development of efficient, stable, economically viable and eco-friendly photocatalysts for hydrogen production is a challenging task. This article reviews the use of nanocomposite in three combinations: metal oxide–metal oxide semiconductor, metal–metal oxide semiconductor and metal chalcogenide–metal oxide core–shell nanostructures. These core–shell structures occur in two forms: a simple form where the photocatalyst is either in the core or the shell or in a more complex system where the core–shell structure comprises a co-catalyst deposited on a semiconducting material. We discuss the design, synthesis and development of semiconductor-based nanocomposite photocatalysts for hydrogen production. The major points are the role of catalytic active sites, the chemical nature of sacrificial agents, the effect of light sources, the variable light intensity and the energy efficiency calculation. For TiO₂-based nanocomposites, the metal oxide or metal co-catalyst loading of 1.0–3.0 wt% was optimal. TiO₂ nanotube–CuO hybrid nanocomposites produce 1,14,000 µmol h^?1 \({\text{g}}^{ - 1}_{\text{cat}}\), whereas TiO₂/Au nanocomposites display 1,60,000 µmol h^?1 \({\text{g}}^{ - 1}_{\text{cat}}\). For core–shell catalysts, a shell thickness of 2–20 nm was found for the best activity, and its performance is as follows: (a) CdS–NiO system produces around 19,949 µmol h^?1 \({\text{g}}^{ - 1}_{\text{cat}}\) and (b) CuO–Cr₂O₃ as co-catalyst immobilized on TiO₂ system produces around 82,390 µmol h^?1 \({\text{g}}^{ - 1}_{\text{cat}}\).     

Bioreduction of nitrate in groundwater using a pilot-scale hydrogen-based membrane biofilm reactor

A long-term pilot-scale H₂-based membrane biofilm reactor (MBfR) was tested for removal of nitrate from actual groundwater. A key feature of this second-generation pilot MBfR is that it employed lower cost polyester hollow fibers and still achieved high loading rate. The steady-state maximum nitrate surface loading at which the effluent nitrate and nitrite concentrations were below the Maximum Contaminant Level (MCL) was at least 5.9 g·N·(m²·d)^?1, which corresponds to a maximum volumetric loading of at least 7.7 kg·N·(m³·d) ^?1. The steady-state maximum nitrate surface area loading was higher than the highest nitrate surface loading reported in the first-generation MBfRs using composite fibers (2.6 g·N·(m²·d)^?1). This work also evaluated the H₂-utilization efficiency in MBfR. The measured H₂ supply rate was only slightly higher than the stoichiometric H₂-utilization rate. Thus, H₂ utilization was controlled by diffusion and was close to 100% efficiency, as long as biofilm accumulated on the polyester-fiber surface and the fibers had no leaks.     

Decolorization of azo dyes by a salt-tolerant Staphylococcus cohnii strain isolated from textile wastewater

The salt-tolerant Staphylococcus cohnii strain, isolated from textile wastewater, has been found effective on decolorizing several kinds of azo dyes with different structures. The optimal conditions for azo dye acid red B (ARB) decolorization by S. cohnii were determined to be pH = 7.0 and 30°C. The decolorization efficiency increased with the increase of the salinity concentration, and around 90% of ARB (100 mg·L^?1) could be decolorized in 24 h when the salinity concentration was up to 50 g·L^?1. Moreover, the strain could still decolorize 19% of ARB in 24 h even when the NaCl concentration was increased to 150 g·L^?1. Meanwhile, the dependence of the specific decolorization rate by S. cohnii on the ARB concentration could be described with Michaelis-Menten kinetics (K _m = 585.7mg·L^?1, V _max = 109.8 mg·g cell^?1·h^?1). The addition of quinone redox mediator, named 2-hydroxy-1,4-naphthoquinone and anthraquinone-2,6-disulfonate, significantly accelerated the decolorization performance of S. cohnii. Furtherly, the activities of azoreductase (0.55 ??mol·mg protein^?1·min^?1) and Nicotineamide adenine dinucleotide-dichlorophenol indophenol (NADH-DCIP) reductase (8.9 ??mol·mg protein^?1·min^?1) have been observed in the crude cell extracts of S. cohnii. The decolorization products of ARB were analyzed by HPLC-MS, and the results indicated the reductive pathway was responsible for azo dye decolorization by S. cohnii.     

Diffusive boundary layers and photosynthesis of the epilithic algal community of coral reefs

The effects of mass transfer resistance due to the presence of a diffusive boundary layer on the photosynthesis of the epilithic algal community (EAC) of a coral reef were studied. Photosynthesis and respiration of the EAC of dead coral surfaces were investigated for samples from two locations: the Gulf of Aqaba, Eilat (Israel), and One Tree Reef on the Great Barrier Reef (Australia). Microsensors were used to measure O₂ and pH at the EAC surface and above. Oxygen profiles in the light and dark indicated a diffusive boundary layer (DBL) thickness of 180–590 μm under moderate flow (~0.08 m s^?1) and >2,000 μm under quasi-stagnant conditions. Under light saturation the oxygen concentration at the EAC surface rose within a few minutes to 200–550% air saturation levels under moderate flow and to 600–700% under quasi-stagnant conditions. High maximal rates of net photosynthesis of 8–25 mmol O₂ m^?2 h^?1 were calculated from measured O₂ concentration gradients, and dark respiration was 1.3–3.3 mmol O₂ m^?2 h^?1. From light–dark shifts, the maximal rates of gross photosynthesis at the EAC surface were calculated to be 16.5 nmol O₂ cm^?3 s^?1. Irradiance at the onset of saturation of photosynthesis, E _k, was <100 µmol photons m^?2 s^?1, indicating that the EAC is a shade-adapted community. The pH increased from 8.2 in the bulk seawater to 8.9 at the EAC surface, suggesting that very little carbon in the form of CO₂ occurs at the EAC surface. Thus the major source of dissolved inorganic carbon (DIC) must be in the form of HCO₃ ^?. Estimates of DIC fluxes across the DBL indicate that, throughout most of the daytime under in situ conditions, DIC is likely to be a major limiting factor for photosynthesis and therefore also for primary production and growth of the EAC.     

Preparation of TiO2/MCM-41 by plasma enhanced chemical vapor deposition method and its photocatalytic activity

Titanium dioxide is coated on the surface of MCM-41 wafer through the plasma enhanced chemical vapor deposition (PECVD) method using titanium isopropoxide (TTIP) as a precursor. Annealing temperature is a key factor affecting crystal phase of titanium dioxide. It will transform an amorphous structure to a polycrystalline structure by increasing temperature. The optimum anatase phase of TiO₂ which can acquire the best methanol conversion under UV-light irradiation is obtained under an annealing temperature of 700°C for 2 h, substrate temperature of 500°C, 70 mL·min^?1 of oxygen flow rate, and 100W of plasma power. In addition, the films are composed of an anatase-rutile mixed phase, and the ratio of anatase to rutile varies with substrate temperature and oxygen flow rate. The particle sizes of titanium dioxide are between 30.3 nm and 59.9 nm by the calculation of Scherrer equation. Under the reaction conditions of 116.8 mg·L^-1 methanol, 2.9 mg·L^?1 moisture, and 75°C of reaction temperature, the best conversion of methanol with UV-light is 48.2% by using the anatase-rutile (91.3/8.7) mixed phase TiO₂ in a batch reactor for 60 min. While under fluorescent light irradiation, the best photoactivity appears by using the anatase-rutile (55.4/44.6) mixed phase TiO₂ with a conversion of 40.0%.     

Seasonal and diel variation in movement rhythms of sand dollar, Peronella lesueuri (Valenciennes 1841), in Cockburn Sound, Western Australia

Rates and direction of movement in the sand dollar Peronella lesueuri were measured in summer and winter in Cockburn Sound, a large coastal embayment in south-western Australia. P. lesueuri was found to have a diurnal activity pattern throughout the year and had a greater movement rate in the summer (mean of 5.3 cm h^?1, day; 3.9 cm h^?1, night) than in the winter (mean of 2.7 cm h^?1, day; 2.0 cm h^?1, night). Seasonal change in temperature and physiological requirements by the sand dollar are the most likely reason for the seasonal differences. Reasons for diurnal variation were not clear. Direction of movement was found to be random at both times of the year. Based on these movement rates, one sand dollar can bioturbate an approximate area of 0.1 m² day^?1 and 36.4 m² year^?1. At a conservative density estimate of 0.5 sand dollars per m² it takes approximately 20 days for the sand dollars to rework the entire area of the sediments in the habitats they occupy.     

Photo- and electro-catalysis for solar disinfection of Escherichia coli-contaminated water using Ag–TiO2/graphite

A titanium dioxide film on a graphite substrate was synthesized by chemical bath deposition from TiCl₄ as precursor and with the surfactant cetyl trimethyl ammonium bromide as a linking and assembling agent. Silver was loaded on the TiO₂ film by electrodeposition at 0.025?A. Water contaminated with Escherichia coli was disinfected under sunlight irradiation by photolysis (Lys), photocatalysis (PC), photoelectrocatalysis (PEC), and electrocatalysis (EC). The highest rate constant, k, was achieved with EC; k was 5.1?×?10^?2 colony forming units (CFU) mL^?1?min^?1. However, auto-oxidation of Ag occurred during EC and PEC. Meanwhile, the rate constant of disinfection by means of PC was lower than EC and PEC, and k was 3.82?×?10^?2 CFU?mL^?1?min^?1. Nevertheless, the auto-oxidation of Ag in the Ag–TiO₂/graphite tablet did not occur during the disinfection process.     

Spatial variations in the N2O emissions and denitrification potential of riparian buffer strips in a contaminated urban river

Spatial variations in the N₂O emissions and denitrification potential of riparian buffer strips (RBS) in a polluted river were examined. The river received large pollutant inputs from urban runoff and wastewater discharge, resulting in impaired water quality in the river and downstream reservoir. The potential for nitrogen removal by RBS was evaluated by measuring in situ N₂O emission fluxes in static closed chambers and sediment denitrification potentials with acetylene inhibition techniques. The results showed that N₂O emission fluxes decreased from the upstream (16.39 μg/(m²·h)) to downstream (0.30 μg/(m²·h)) sites and from the water body to upland sites. The trend in decreasing N₂O emission fluxes in the downstream direction was mainly associated with sediment/soil textures (clay loam→sandy soil) and sediment/soil water contents and was also related to the vegetation along the RBS and nutrients in the sediments/soils. The correlation coefficient was highest (r=0.769) between the N₂O emission flux and sediment/soil water content. Sediment/soil denitrification potentials under N-amended and ambient conditions were higher (highest 32.86 mg/(kg·h)) for the upstream sites, which were consistent with in situ N₂O flux rates.     

Biodegradation of carbofuran in sequencing batch reactor augmented with immobilised Burkholderia cepacia PCL3 on corncob

The performance of sequencing batch reactors (SBRs) augmented with immobilised Burkholderia cepacia PCL3 on corncob for biodegradation of carbofuran in basal salt medium (BSM) was studied. A 2.0-L SBR with a working volume of 1.5 L was operated for a total cycle of 48 h, consisting of 1.0 h fill phase, 46 h react phase and 1.0 h decant phase. The initial pH of the feed medium was 7.0. Air was fed into the reactor at a controlled flow rate of 600 mL·min ^?1. The effect of hydraulic retention time (HRT) (14 to 6 days) on carbofuran-degradation efficiency was investigated at a carbofuran concentration in the feed medium of 20 mg·L ^?1. The shortest HRT resulting in complete degradation of carbofuran was 8 days. At 75% of the optimum HRT (6 days), the effects of biostimulation using organic amendments, i.e. molasses, cassava pulp, rice bran and spent yeast, and the effect of carbofuran concentration in the feed medium (20–80 mg·L ^?1) were investigated. The optimum conditions for SBRs were an initial carbofuran concentration of 40 mg·L ^?1 and 0.1 g·L ^?1 of rice bran as a biostimulated amendment. Complete degradation of carbofuran with a first-order kinetic constant (k ₁) of 0.044 h^?1 was achieved under these optimum conditions.     

Solar-induced generation of singlet oxygen and hydroxyl radical in sewage wastewaters

Singlet oxygen (¹O₂) and hydroxyl radical (·OH) play an important role in the degradation of pollutants in surface waters. However, the mechanism underlying the photochemical generation of ¹O₂ and ·OH in wastewaters is poorly known. Here we studied the photo-induced generation of ¹O₂ and ·OH in different sewage treatment plant units. The correlation between the generation of ¹O₂ and ·OH and the water constituents was discussed. Our results show that in sewage units the ¹O₂ formation rate ranges from 2.19 × 10^?8 to 6.74 × 10^?8 mol L^?1 s^?1, and the ·OH formation rate ranges from 1.7 × 10^?11 to 3.06 × 10^?10 mol L^?1 s^?1. The average ¹O₂ formation rates in the various sewage units are similar to those in wetland and estuarine waters containing rich dissolved organic matter and 2–4 times higher than those in lake and seawater samples. The average ·OH formation rates of the sewage units are 5–50 times higher than for other water samples reported. The ·OH generation rate increased with the iron content with a correlation coefficient of 0.85, which indicates that the photo-Fenton reaction plays a dominant role in ·OH generation in sewage wastewater.     

Occurrence of benzotriazoles (BTRs) in indoor air from Albany,New York,USA, and its implications for inhalation exposure

Despite the widespread use of benzotriazoles as corrosion inhibitors in many household goods, studies on the occurrence of these compounds in indoor air are scarce. In this study, five benzotriazole derivatives were measured in 83 indoor air samples collected from various locations in Albany, New York, USA. Benzotriazoles were found in a majority of the indoor air samples, and the concentrations of their sum in bulk (vapor plus particulate phases) indoor air ranged from below the method limit of quantification to 492 ng·m^?3 (geometric mean: 5.8 ng·m^?3). The highest geometric mean concentration was found in air samples collected in parking garages (155 ng·m^?3), followed by barbershops (13.6), public places (11.5), auto repair shops (5.2), automobiles (4.5), homes (4.5), offices (3.7), and laboratories (2.8). Inhalation exposure to benzotriazoles was calculated on the basis of the measured geometric mean concentrations and air inhalation rate. The highest exposure dose was found for teenagers, with a geometric mean inhalation exposure dose of 79 ng·day^?1. The body-weight normalized exposure dose, however, was the highest for infants, at 3.2 ng·(kg bw)^?1·day^?1.     

Relationships between loading rates and nitrogen removal effectiveness in subsurface flow constructed wetlands

Nitrogen removal of wetlands under 40 different inflow loadings were studied in the field during 15 months. The removal efficiency of four different sets of beds, namely the reed bed, the Zizania caduciflor bed, the mixing planting bed, and the control bed were studied. The outflow loading and total nitrogen (TN) removal rate of these beds under different inflow loadings and pollution loadings were investigated. The inflow loadings of 4 subsurface flow systems (SFS) ranged from 400 to 8000 mg·(m²·d)^?1, while outflow loadings were less than 7000 mg·(m²·d)^?1. The results showed that the inflow and outflow loading of TN removal rate in SFS presented an obvious linear relationship. The optical inflow loading to run the system was between 2000 to 4000 mg·(m²·d)^?1. Average removal rate was between 1062 and 2007 mg·(m²·d)^?1. SFS with plant had a better removal rate than the control. TN removal rates of the reed and Zizania caduciflora bed were 63% and 27% higher than the control bed, respectively. The results regarding the TN absorption of plants indicated that the absorption amount was very limited, less than 5% of the total removal. It proved that plants clearly increase TN removal rates by improving the water flow, and increasing the biomass, as well as activities of microorganisms around the roots. The research provided a perspective for understanding the TN removal mechanism and design for SFS.     

Nano-titanium dioxide (TiO2)-induced changes affecting Cu2+-mediated alterations in bacterium Bacillus subtilis and α-amylase

Titanium dioxide (TiO₂) nanoparticles possess the potential to coexist with Copper (Cu²⁺) in soil. The individual and combined toxicity of these two chemicals was evaluated using the bacterium Bacillus subtilis, a known soil model bacterium. Cu²⁺ (6.25–50?µg?mL^?1) alone produced toxicity to bacteria as evidenced by the decreased cell viability and deceased α-amylase production. The addition of TiO₂ (50?mg?mL^?1) enhanced the Cu²⁺-induced decrease in cell viability but elevated amylase activity. TiO₂ did not markedly affect the growth rate and lag period. A primary cause of TiO₂ increasing Cu²⁺ toxicity is presumed to be associated with hydroxyl radical formation, while increased amylase activity is considered to arise from Cu²⁺ facilitating TiO₂ degradation ability.     

Immobilized Lentinus edodes residue as absorbent for the enhancement of cadmium adsorption performance

To investigate the potential use of Lentinus edodes (L. edodes) residue for Cd²⁺ adsorption, poly alcohol Na alginate (PVA) was applied to immobilize it. The parameters including contact time, pH, adsorbent dosages, and coexisting metal ions were studied. The suitable pH for immobilized L. edodes was 4?C7 wider than that for raw L. edodes (pH 6?C7). In the presence of Pb²⁺ concentration varying from 0 to 30 mg·L^?1, the Cd²⁺ adsorption ratios declined by 6.71% and 47.45% for immobilized and raw L. edodes, respectively. While, with the coexisting ion Cu²⁺ concentration varied from 0 to 30 mg·L^?1, the Cd²⁺ adsorption ratios declined by 12.97% and 50.56% for immobilized and raw L. edodes, respectively. The Cd²⁺ adsorption isotherms in single-metal and dual-metal solutions were analyzed by using Langmuir, Freundlich, and Dubinin-Radushkevich models. The Cd²⁺ adsorption capacities (q _m) in single-metal solution were 6.448 mg·L^?1 and 2.832 mg·L^?1 for immobilized and raw L. edodes, respectively. The q _m of immobilized L. edodes were 1.850 mg Cd·g^?1 in Cd²⁺ + Pb²⁺ solution and 3.961 mg Cd·g^?1 in Cd²⁺ + Cu²⁺ solution, respectively. The Cd²⁺ adsorption processes subjected to both adsorbents follow pseudo-second-order model. Mechanism study showed the functional group of L. edodes was -OH, -NH, -CO, and PVA played an important role in metal adsorbing. Mining wastewater treatment test showed that PVA-SA-immobilized L. edodes was effective in mixed pollutant treatment even for wastewater containing metal ions in very low concentration.     

Toxicokinetics,metabolism, and microsomal studies of chlorpropham in rats

A study on the toxicokinetic behavior, metabolism of chlorpropham, and its effect on cytochrome P₄₅₀ from liver microsomes was carried out in albino rats after a single and consecutive oral administration at 500?mg?kg^?1 body weight for 10 and 20 days. Chlorpropham was detected in the blood at 0.08?h (11.43?±?1.72?µg?mL^?1) reaching a maximum concentration at 2?h (30.90?±?2.55?µg?mL^?1) and a minimum at 48?h (1.95?±?0.20?µg?mL^?1) after a single oral administration of 500?mg?kg^?1. The absorption rate constant (K _a) was 0.66?±?0.48?h^?1. The Vd _area (18.01?±?2.78?L?kg^?1) and t _1/2 β (12.23?±?1.96?h) values suggested a wide distribution and long persistence of the compound in the body, respectively. The higher Cl_R (0.82?±?0.00?L?kg^?1?h^?1) compared to Cl_H (0.18?±?0.02?L?kg^?1?h^?1) value indicated that a major portion of chlorpropham was excreted through the urine (30%) compared to the faeces (2.81%). Chlorpropham residue was detected in all tissues of rat at 0.25?h while its metabolite, meta-chloroaniline was detected in liver, kidney, heart, lung, and spleen tissue at 0.25?h. Meta-chloroaniline was not detected in skeletal muscle, brain, fat, and stomach tissue at any time of the observation period. Maximum concentrations of chlorpropham and meta-chloroaniline were detected at 2?h (except in the spleen), and minimum concentrations of chlorpropham at 24 (heart, lung, spleen, skeletal muscle, and stomach) and 48?h (liver, kidney, brain, and fat tissue) respectively; and meta-chloroaniline at 24?h (except heart and spleen). The tissue half-life of chlorpropham in rat varied from 3.80 to 11.60?h. Repeated oral administration of chlorpropham at 500?mg?kg^?1 for 10 and 20 days caused an induction of the liver microsomal pellet of rat.     

Suppression of inhibition of substrate photodegradation by scavengers of hydroxyl radicals: the solvent-cage effect of bromide on nitrate photolysis

In this paper we show that bromide scavenges the ^·OH radicals formed upon photolysis of nitrate, before they leave the solvent cage. Bromide can thus inhibit the in-cage recombination between ^·OH and ^·NO₂. The consequence is an increased generation of ^·NO₂ and nitrite and of Br₂ ^?· + ^·OH, compared to ^·OH alone in the absence of bromide. We show that this effect compensates for the lower reactivity of Br ₂ ^?· compared to ^·OH toward certain organic substrates, e.g. phenol and tryptophan. Our findings could lead to a deep revision of the present views of the role of bromide in saltwater photochemistry.