Photoelectrocatalytic degradation of Ag-cyanide complexes and synchronous recovery of metallic Ag driven by TiO2 nanorods array photoanode combined with titanium cathode.

A photoelectrocatalytic (PEC) system for the decomposition of Ag-cyanide complexes synchronously with Ag recovery was established using the titanium dioxide nanorods (TiO2 NRs) as photoanode and the titanium plate as cathode. The removal efficiency of total cyanide was 76.58%, and the recovery ratio of Ag achieved 84.48% at the applied bias potential of 1.0 V vs SCE in the PEC process. During the reaction, the surface variations and photo-electric properties of TiO2 NRs photoanode or titanium cathode were characterized by SEM-EDS, XPS, and photoelectronic analyses. It was indicated that Ag2O and metallic Ag were deposited onto the TiO2 NRs photoanode and titanium cathode, respectively. Specifically, the in situ generated Ag2O on the TiO2 NRs photoanode facilitated the separation of the photogenerated charge carriers and enhanced the visible-light response, thus improving its PEC catalytic activity toward cyanide destruction. Combined with the results of active species quenching experiments, the mechanism of Ag-cyanide complexes decomposition and metallic Ag recovery by the PEC process was proposed.

Promoting sun light-induced photocatalytic degradation of toxic phenols by efficient and stable double metal cyanide nanocubes.

Aromatic substituted phenols and their by-products discharged from numerous industries are of environmental concern due to their toxic, carcinogenic, recalcitrant, and bioaccumulating properties. Therefore, their complete removal from waters by low-cost, efficient, environmentally friendly nanomaterial-based treatment techniques is desirable. Double metal cyanide complexes (DMCC) are the extremely useful heterogeneous and recoverable catalyst. Hence, green route has been developed for several DMCC and their photocatalytic efficiency was evaluated for degradation of toxic phenols. Herein, nanocubes for hexacyanocobaltate of iron (FeHCC ~ 200 nm), nickel (NiHCC < 10 nm), and zinc (ZnHCC ~ 500 nm) were synthesized after employing Aegle marmelos. Subsequently, at neutral pH and sunlight irradiation, 15 mg of catalysts were able to degrade the maximum extent of phenols (1 × 10-4 M) in the order: 3-aminophenol (96% ZnHCC > 94% FeHCC > 93% NiHCC) > phenol (94% ZnHCC > 92% FeHCC > 91% NiHCC) > 2,4-DNP (92% ZnHCC > 91% FeHCC > 90% NiHCC). This is attributed to highest basicity of 3-aminophenol containing excess of free electrons. Highest catalytic potential of ZnHCC (Xm = 0.54-0.43 mg/g) is because of its highest surface area and negative zeta potential along with sharp morphology and crystallinity. Adsorption of phenols over catalyst was statistically significant with Langmuir isotherms (R2 ≥ 0.96; p value ≤ 0.05). Small and non-toxic by-products like oxalic acid, benzoquinone, (Z)-hex-3-enedioic acid, (Z)-but-2-enal, and (Z)-4-oxobut-2-enoic acid were identified in GC-MS. Degradation modes involving hydroxylation, oxidative skeletal rearrangement, and ring opening clearly supported enhanced oxidation of phenols by •OH. Overall, due to greater active sites, high surface activity, low band gap, and semiconducting nature, DMCC revealed promising potential for solar photocatalytic remediation of wastewater.

Photolabile ruthenium complexes to cage and release a highly cytotoxic anticancer agent.

CHS-828 (N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N″-4-pyridyl guanidine) is an anticancer agent with low bioavailability and high systemic toxicity. Here we present an approach to improve the therapeutic profile of the drug using photolabile ruthenium complexes to generate light-activated prodrugs of CHS-828. Both prodrug complexes are stable in the dark but release CHS-828 when irradiated with visible light. The complexes are water-soluble and accumulate in tumour cells in very high concentrations, predominantly in the mitochondria. Both prodrug complexes are significantly less cyototoxic than free CHS-828 in the dark but their toxicity increases up to 10-fold in combination with visible light. The cellular responses to light treatment are consistent with release of the cytotoxic CHS-828 ligand.

Enhanced photoelectrocatalytic decomposition of copper cyanide complexes and simultaneous recovery of copper with a Bi2MoO6 electrode under visible light by EDTA/K4P2O7.

Simultaneous photoelectrocatalytic (PEC) oxidation of cyanides and recovery of copper in a PEC reactor with a Bi(2)MoO(6) photoanode was investigated at alkaline conditions under visible light irradiation. The surface variation of the Bi(2)MoO(6) photoanode and titanium cathode was characterized. The Cu mass distribution onto the anode, in the solution, and onto the cathode was fully investigated. In the individual PEC oxidation of copper cyanides, the formation of a black copper oxide on the anode occurred. By keeping the initial cyanide concentration at 0.01 mM, the effect of EDTA/K(4)P(2)O(7) was examined at different molar ratios of EDTA/K(4)P(2)O(7) to cyanide. It was indicated that the oxidation of cyanides increased and simultaneous copper electrodeposition with zero value onto the cathode was feasible at pH 11. Under the optimal conditions, the total cyanide concentration was lowered from 250 to 5.0 mg/L, and the Cu recovery efficiency deposited onto the cathode was higher than 90%. Cyanate was the only product. The role of the photogenerated hole in the oxidation of cyanide ions was confirmed.

Scale-up study of a multiphase photocatalytic reactor--degradation of cyanide in water over TiO2.

This paper provides an integrated view on various aspects of reactor design for photocatalytic reactions and presents a scale-up study of photocatalytic reactors. This study focuses on degrading organic pollutants in the effluent of an integrated gasification coal combustion plant over TiO2, with the target of degrading cyanide to below its allowable emission threshold set by European legislation. Here, we show the interplay of different efficiencies that affect the overall apparent photonic efficiency and the reactor volume required to achieve a certain objective in conversion. The chosen reactor configuration is rectangular slurry-bubble-columns-in-series to ensure a good mass transfer rate per photoreactor while approaching plug-flow behavior as a sum, and a high reactor surface-area-to-volume ratio for a good capture of incident photons. We consider a simple 1D photonic description of a photoreactor, in the direction of incident solar light, and implement a bidirectional scattering model for photocatalytic particles and bubbles to calculate the local rate of photon absorption and the photon absorption efficiency in the photoreactor. We show that, implementing the principles of process intensification, the large scale degradation of cyanide to below European emission limits is achievable.

Photo/photochemical oxidation of cyanide and metal-cyanide complexes: ultraviolet A versus ultraviolet C.

Degradation of free cyanide (CN(-)), weak-acid dissociable (WAD) (Zn(CN)4(2-), Cu(CN)3(2-)) and strong-acid dissociable (SAD) (Fe(CN)6(4-) cyanide complexes by photo and photochemical oxidation with ultraviolet (UV) light and H2O2 was investigated. The experiments were performed in batch reactors under ultraviolet A (UVA; 395 nm) and ultraviolet C (UVC; 254 nm) light; the degradation efficiency was followed in terms of free cyanide, complex and metal concentrations. UVC and UVA photo-oxidations were found to be equally effective in CN(-) and WAD degradation, while the degradation of the SAD complex was more difficult for both UV wavelengths, and UVC was more effective. The initial pH of the solution has influenced the degradation of all cyanide species and the optimum initial pH was evaluated as 10.5 for CN(-) and Cu(CN)3(2-); 12.0 for Zn(CN)4(2-) and 9.0 for Fe(CN)6(4-) degradation. Photochemical oxidation using H202 provided higher degradation at shorter durations with both UVA and UVC. Time-dependent variations in free cyanide and metal concentrations have indicated that metal-cyanide complexes are firstly degraded into metal and CN(-) ions, followed by oxidation of CN(-) ions, while metals in the system were partially removed as hydroxide precipitates. Therefore, depending upon the effluent requirements, the studied UV photo/photochemical oxidations were offered as either a pre-treatment method for the separation of metal and the cyanide, or as an oxidation technology to degrade especially WAD complexes and CN(-). Estimated operational cost of photo-oxidation by UVC was 1.6-2.5-fold higher than UVA degradation, although degradation times were close. In the photochemical oxidation with H2O2, the operational costs of UVC and UVA degradation were closer, owing to peroxide costs, but UVC was still more expensive.

Effects of UV 254 irradiation on residual chlorine and DBPs in chlorination of model organic-N precursors in swimming pools.

Ultraviolet (UV) irradiation is commonly applied as a secondary disinfection process in chlorinated pools. UV-based systems have been reported to yield improvements in swimming pool water and air chemistry, but to date these observations have been largely anecdotal. The objectives of this investigation were to evaluate the effects of UV irradiation on chlorination of important organic-N precursors in swimming pools. Creatinine, L-arginine, L-histidine, glycine, and urea, which comprise the majority of the organic-N in human sweat and urine, were selected as precursors for use in conducting batch experiments to examine the time-course behavior of several DBPs and residual chlorine, with and without UV(254) irradiation. In addition, water samples from two natatoria were subjected to monochromatic UV irradiation at wavelengths of 222 nm and 254 nm to evaluate changes of liquid-phase chemistry. UV(254) irradiation promoted formation and/or decay of several chlorinated N-DBPs and also increased the rate of free chlorine consumption. UV exposure resulted in loss of inorganic chloramines (e.g., NCl(3)) from solution. Dichloromethylamine (CH(3)NCl(2)) formation from creatinine was promoted by UV exposure, when free chlorine was present in solution; however, when free chlorine was depleted, CH(3)NCl(2) photodecay was observed. Dichloroacetonitrile (CNCHCl(2)) formation (from L-histidine and L-arginine) was promoted by UV(254) irradiation, as long as free chlorine was present in solution. Likewise, UV exposure was observed to amplify cyanogen chloride (CNCl) formation from chlorination of L-histidine, L-arginine, and glycine, up to the point of free chlorine depletion. The results from experiments involving UV irradiation of chlorinated swimming pool water were qualitatively consistent with the results of model experiments involving UV/chlorination of precursors in terms of the behavior of residual chlorine and DBPs measured in this study. The results indicate that UV(254) irradiation promotes several reactions that are involved in the formation and/or destruction of chlorinated N-DBPs in pool settings. Enhancement of DBP formation was consistent with a mechanism whereby a rate-limiting step in DBP formation was promoted by UV exposure. Promotion of these reactions also resulted in increases of free chlorine consumption rates.

The stretching frequencies of bound alkyl isocyanides indicate two distinct ligand orientations within the distal pocket of myoglobin.

The FTIR spectra for alkyl isocyanides (CNRs) change from a single nu(CN) band centered at approximately 2175 cm(-1) to two peaks at approximately 2075 and approximately 2125 cm(-1) upon binding to sperm whale myoglobin (Mb). The low- and high-frequency peaks have been assigned to in and out conformations, respectively. In the in conformation, the ligand is pointing toward the protein interior, and the distal His64(E7) is in a closed position, donates a H-bond to the bound isocyano group, enhances back-bonding, and lowers the C-N bond order. In the out conformation, the ligand side chain points toward solvent through a channel opened by outward rotation of His64. Loss of positive polarity near the binding site causes an increase in C-N bond order. Support for this interpretation is threefold: (1) similar shifts to lower frequency occur for MbCO complexes when H-bond donation from His64(E7) occurs; (2) only one peak at approximately 2125 cm(-1), indicative of an apolar environment, is observed for CNRs bound to H64A or H64L Mb mutants or to chelated protoheme in soap micelles; and (3) the fraction of in conformation based on FTIR spectra correlates strongly with the fraction of geminate recombination after nanosecond laser photolysis. The in alkyl side chain conformation causes the photodissociated ligand to be "stuck" in the distal pocket, promoting internal rebinding, whereas the out conformation inhibits geminate recombination because part of the ligand is already in an open E7 channel, poised for rapid escape.

Activated sludge respirometry to assess solar detoxification of a metal finishing effluent.

Inhibition of the respiration of activated sludge has been tested as a convenient method to estimate toxicity of aqueous solutions containing copper and cyanide, such as metal finishing effluents; according to this method, an EC50 of 0.5 mg/l was determined for CN(-) and 3.0 mg/l for copper. Solar detoxification of cyanide-containing solutions was studied using TiO2, but this process was unfavourable because of the inhibitory role that plays the copper ions present in real effluents on the oxidation of cyanide. On the other hand, the oxidative effect of hydrogen peroxide was greatly enhanced by Cu2+ and solar irradiation, as complete elimination of free and complexed cyanide could be accomplished, together with precipitation of copper, in experiments carried out at pilot plant scale with real metal finishing effluents. Under these conditions, total detoxification was achieved according to respirometric measurements although some remaining toxicity was determined by more sensitive Vibrio fischeri luminescent assay.

Photocatalytic degradation of pollutants from Elcogas IGCC power station effluents.

The aim of this work is to improve the quality of water effluents coming from Elcogas IGCC power station (Puertollano, Spain) with the purpose of fulfilling future more demanding normative, using heterogeneous photocatalytic oxidation processes (UV/H(2)O(2)/TiO(2) or ZnO). The efficiency of photocatalytic degradation for the different catalysts (TiO(2) and ZnO) was determined from the analysis of the following parameters: cyanides, formates and ammonia content. In a first stage, the influence of two parameters (initial concentration of H(2)O(2) and amount of catalyst) on the degradation kinetics of cyanides and formates was studied based on a factorial experimental design. pH was always kept in a value >9.5 to avoid gaseous HCN formation. The degradation of cyanides and formates was found to follow pseudo-first order kinetics. Experimental kinetic constants were fitted using neural networks (NNs). The mathematical model reproduces experimental data within 90% of confidence and allows the simulation of the process for any value of parameters in the experimental range studied. Moreover, a measure of the saliency of the input variables was made based upon the connection weights of the neural networks, allowing the analysis of the relative relevance of each variable with respect to the others. Results showed that the photocatalytic process was effective, being the degradation rate of cyanides about five times higher when compared to removal of formates. Finally, the effect of lowering pH on the degradation of formates was evaluated after complete cyanides destruction was reached (10 min of reaction). Under the optimum conditions (pH 5.2, [H(2)O(2)]=40 g/l; [TiO(2)]=2g/l), 100% of cyanides and 92% of initial NH(3) concentration are degraded after 10 min, whereas 35 min are needed to degrade 98% of formates.

Water absorption and desorption from the dipole ordered polymer poly(methylvinylidene cyanide).

From thermal desorption studies, we find evidence that absorbed water in the bulk of poly(methylvinylidene cyanide) is more weakly bound than is the case for copolymer films of poly(vinylidenefluoride-trifluoroethylene). Ultraviolet laser enhanced thermal desorption of absorbed water exhibits little light polarization dependence for poly(methylvinylidene cyanide) in contrast to absorbed water in copolymer films of poly(vinylidenefluoride-trifluoroethylene). The implications of these differences are discussed.

The radiolysis of aqueous ammonium cyanide: polymers of interest to chemical evolution studies.

Some of the polymers isolated from the mixture of products obtained upon irradiation of dilute oxygen-free solutions of NH4CN with gamma rays from a 60Co source were examined. Their molecular weights were estimated to be in the range 4000-20000 daltons; elements of their structure were inferred from chemical and spectroscopic studies; and their interactions with nucleic acid components were examined. Significance of these results for chemical evolution studies is summarized.

The radiolysis of aqueous ammonium cyanide: compounds of interest to chemical evolution studies.

Oxygen-free aqueous solutions of NH4CN (0.1 M, pH9) were exposed to gamma rays from a 60Co source, the mixture of nonvolatile products was fractionated, and the fractions were analyzed. The procedures were chosen to make effective investigations of radiolytic products, and to minimize the contributions of chemical changes which are known to occur in aqueous solution in the absence of ionizing radiation. It has been found that the main constituents are: urea, 25.9%; an oligomer, very likely oligoimine (18.4%); and several fractions (about 50%) which release amino acids on hydrolysis. These fractions differ considerably, as shown by amino acid assay, enzymatic digestion, IR spectra, and biuret reaction. All these tests were found to be positive for two fractions; in two further fractions the enzymatic cleavage was absent, but other tests were positive. Negative enzymatic and biuret tests, and no bands characteristic of amide or peptide, were found for a fraction whose hydrolysate consisted of 55% glycine. Although most of the isolated materials were found to be composite, the results of the analyses were sufficient for getting a reliable over-all picture of the chemical action of the ionizing radiation. The role of free radicals in reactions leading to the formations of radiolytic products was considered.

Evidence for amino acids in hydrolysates of compounds formed by ionizing radiations. I. Aqueous solutions of HCN, NH4CN, and NaCN.

Dilute, 02-free aqueous cyanides were exposed to multikilorad doses of a radioactive cobalt source. After the removal of unreacted cyanides and of volatile radiolytic products, the residue was hydrolyzed and the resulting material analyzed for amino acids. The results show the presence of five protein amino acids and five amino acids which do not occur in natural proteins. The amino acids of enantiomeric derivatives separated on an optically active column, appeared to consist of approximately equal amounts of D and L isomers. Radiation-chemical yields of amino acids were determined at various radiation doses. The results obtained support the previous findings that the free-radical initiated process is the source of oligomers which on hydrolysis release the amino acids.

Infrared spectral characterization of peptidic material produced by ionizing radiation in aqueous cyanides.

Oligomers formed by ionizing radiation in aqueous cyanide solutions, under various experimental conditions, have been characterized by infrared spectroscopy. IR bands appear in the region known to be characteristic for amides and peptides. The results are discussed in relation to radiation-induced formation of peptidic material and the potential role of ionizing radiation as an energy source for some processes in prebiotic molecular evolution.