Oxidant Consumption Research Articles

Preparation of high solid content oxidized starch by acid pretreatment–H2O2 oxidation and its performance as the ligand in zirconium tanning

Highly-oxidized starch (HOS) is an excellent ligand for zirconium tanning in leather making. However, oxidation reaction can only be undertaken in diluted solution due to the high viscosity of starch, which leads to high oxidant consumption and low solid content of HOS, and therefore greatly limits its industrial application. Starch was predegraded by using HCl followed by H2O2 oxidation for preparing a practical oxidized starch (OST) ligand with high solid content. HCl (5%) remarkably reduced the viscosity of starch and simplified the subsequent oxidation, resulting in a decrease in H2O2 dosage from 60% to 40% and an increase in solid content from 10% to 38%. HCl broke the α-(1–4) glycosidic bond between glucose units, and H2O2 oxidation led to the generation of abundant carboxyl groups in OST. The OST with moderate molecular weight (Mw 5609 g/mol) and carboxyl content (6.48 mmol/g) made the tanning performance of OST–Zr comparable to those of HOS–Zr and chrome tanning agents. Therefore, this work gives new insights into the crop-polysaccharides based ligands application and exhibits huge potential for promoting industrial applications of zirconium tanning.

How to recover iodine more efficiently? Extraction of triiodide

An efficient process was proposed for the recovery of iodine via solvent extraction of triiodide (I3−) when 21% of I− was oxidized. I3− and I− rather than I2 were confirmed to be extracted into the organic phase containing Alamine336. It was found that the coordination effect was an important contributor in the extraction process. The extraction rate significantly increased with the increase of the H2O2 dosage, the phase volume ratio and the extractant concentration, whereas it decreased with the increase of equilibrium pH and temperature. The extraction mechanism was established by UV–vis spectra analysis and saturation extraction test. The extracted species were approximately 27% of I3− and 73% of I−, and each of them was bonded with an extractant molecule respectively. High selectivity was also achieved as the molar ratio of I/Cl increased by 600 times after extraction. Compared with the extraction of simple iodide, the novel process exhibited a much higher efficiency (91% vs 63%). Moreover, the novel process also has an advantage over conventional air blowing with less oxidant consumption and milder temperatures.

Wastewater treatment of industrial enterprises from copper compounds by feritization

The article is devoted to solving an urgent problem - the development of effective methods of water purification from heavy metal ions from industrial wastewater.
 Today more emphasis on technologies that allow recycling of precious metals, the organization of return water supply and receipt safe disposal of sludge. Experimental studies of copper ions extraction from industrial wastewater of galvanic production by ferritization method have been carried out. The process of formation of ferromagnetic compounds of copper and iron has been studied. The results of X-ray diffraction analysis of the mineralogical composition of the samples and phase transformations that occur during aging and during the experiment are presented. The lattice constant of the α-ferite phase is calculated. X-ray diffraction analysis confirmed the presence of ferite compounds and metallic copper. In this case, in the process of "aging" of the samples, the amount of the ferrite phase and metallic copper increases. Electron microscopic analysis confirmed that in the surface layer changed due to the formation of new phases, copper-containing iron oxides, the formation of cement copper and cuprospinel simultaneously exist.
 The influence on the course of the ferritization process of its conditions - the concentration and ratio of copper and iron ions, temperature, pH of the medium, the consumption of oxidant - oxygen is studied. The optimal parameters of the ferritization process for wastewater treatment from copper with an initial concentration of up to 10 g / l are determined. The possibility of formation of copper ferrite without aeration at a temperature of 200 C is shown.
 The study of physicochemical properties of sediments formed during ferritization is performed.
 Studies have shown that the residual concentration of copper in the solution after the application of the proposed technology is in the range from 0.14 to 0.6 mg / l. The efficiency of copper removal is 99.98%.
 It is established that at the process temperature within 50… 700 C, the ratio
 Cu: Fe = 1: 2.7, pH = 8.8… 10.5 and aeration intensity 4… 8 l / min precipitates are formed, which consist in the vast majority of ferrites and metallic copper.

Insights into the synergistic role of catalytic ceramic membranes for ozone and peroxymonosulfate activation towards effective recalcitrant micropollutant degradation and mineralization

This work evaluated the application of catalytic ceramic membrane (Me-CCM, Me = Ce or Co) functionalized with Me-doped TiOx catalytic filtration layer and MeOx nanocatalysts impregnated substrate in the Hybrid Oxidation Separation Technology (HOST) for recalcitrant micropollutant (MP) degradation. The architectural design of the Me-CCM was aimed to enhance the oxidant utilization for the targeted MP degradation and mineralization via the synergism of membrane separation and advanced oxidation process (AOP) within the hybrid membrane reactor. The self-cleaning property of the Me-CCMs was first investigated with humic acid as foulant. A series of comparison studies was conducted with the Me-CCMs employed for degradation of a MP mixture (bisphenol A (BPA), benzotriazole (BTA), clofibric acid (CA), N,N-diethyl-m-toluamide (DEET) and sulfamethoxazole (SMX)) in the HOST process operated under a continuous dead-end filtration mode and dosed with O3 or peroxymonosulfate (PMS). The Ce-CCM/O3 HOST process could effectively degrade and mineralize the MPs with a low specific oxidant consumption of 0.7 M O3(aq) M−1 TOC removal, whereas the Co-CCM/PMS HOST process exhibited selective BPA and SMX degradation. The reactive oxygen species (ROS), including HO•, O2•−, SO4•− and 1O2 were identified by electron paramagnetic resonance spectrometer (EPR), ROS scavenging and molecular probing experiments. The robustness of the HOST system was tested with real water matrices obtained from the local water treatment and reclamation plants. The bromate formation potential was also investigated in the hybrid processes, in which the short contact time within the Me-CCM porous structure could effectively inhibit the bromate formation.

Solar-driven free chlorine advanced oxidation process for simultaneous removal of microcontaminants and microorganisms in natural water at pilot-scale

Contamination of natural water (NW) by emerging contaminants has been widely pointed out as one of the main challenges to ensure high-quality drinking water. Thus, the effectiveness of a solar-driven free chlorine advanced oxidation process simultaneously investigating the elimination of six organic microcontaminants (OMCs) and three bacteria from NW at a pilot-scale was evaluated in this study. Firstly, the solar/free chlorine process was studied at lab-scale using a solar simulator to evaluate the effect of free chlorine concentration (0.5–10 mg L−1) on OMC degradation and generation of toxic oxyanions (e.g., ClO3− ions). Thus, the best free chlorine concentration observed was applied for the simultaneous removal of OMCs and pathogens under natural solar light at pilot scale. At lab-scale, the solar/free chlorine (2.5 mg L−1) process achieved 80% of total degradation in 5 min (1.4 kJ L−1 of accumulative UV energy) with an oxidant consumption of 0.3 mg L−1 and without ClO3− generation. Similar results were attained under natural solar irradiation at a pilot-scale. For all bacteria strains, the legally required detection limit (DL = 1 CFU 100 mL−1) for reclaimed water reuse was attained in a short contact time. Still, more importantly, the solar/free chlorine (2.5 mg L−1) process effectively avoided the possible bacterial regrowth in the post-treated sample after six days. Finally, the combination of free chlorine with solar irradiation provided a simple and energy-efficient process for OMC and bacteria removal in NW at a pilot-scale.

Kinetic Modeling-Assisted Mechanistic Understanding of the Catalytic Ozonation Process Using Cu-Al Layered Double Hydroxides and Copper Oxide Catalysts.

In this study, copper aluminum layered hydroxides (Cu-Al LDHs) and copper oxide (CuO) were utilized as catalysts for heterogeneous catalytic ozonation (HCO). Target compounds oxalate and formate were used with removal by adsorption and oxidation quantified to elucidate the role of the catalyst in contaminant removal. Oxidation of oxalate mostly occurred on the catalyst surface via interaction of surface oxalate complexes with surface-located oxidants. In contrast, the oxidation of formate occurred in the bulk solution as well as on the surface of the catalyst. Measurement of O3 decay kinetics coupled with fluorescence microscopy image analysis corresponding to 7-hydroxycoumarin formation indicates that while surface hydroxyl groups in Cu-Al LDHs facilitate slow decay of O3 resulting in the formation of hydroxyl radicals on the surface, CuO rapidly transforms O3 into surface-located hydroxyl radicals and/or other oxidants. Futile consumption of surface-located oxidants via interaction with the catalyst surface was minimal for Cu-Al-LDHs; however, it becomes significant in the presence of higher CuO dosages. A mechanistic kinetic model has been developed which adequately describes the experimental results obtained and can be used to optimize the process conditions for the application of HCO.

The effect of sulfate half-ester groups on cellulose nanocrystal periodate oxidation

Periodate oxidation introduces aldehyde functionality to cellulose. The use of dialdehyde cellulose has been demonstrated for crosslinking and as a chemical intermediate towards functionalized cellulose. Commercially available cellulose nanocrystals (CNCs) typically carry a surface sulfate half-ester functionality, which results from their manufacture via sulfuric acid hydrolysis and subsequent esterification. The sulfate half-ester group is a bulky group carrying a net negative charge above pH 2 that modifies the colloidal and electro-chemical properties of the CNCs. Periodate oxidation is regioselective to the bond between carbons in positions 2 and 3 in the anhydroglucose unit while the sulfate half-ester groups are mostly considered to be located in carbon in position 6. This regioselectivity could be the reason why the role played by the sulfate half-ester group on modification by periodate oxidation has not previously been elucidated. Here, the influence of the sulfate half-ester on the oxidation of CNCs, which is shown to steer the oxidation kinetics and the properties of the resulting materials, is studied. Conventional physicochemical analysis of the oxidant consumption is accompanied by elemental analysis, Fourier-transform infrared, X-ray photoelectron and solid-state nuclear magnetic resonance spectroscopy, and wide-angle x-ray scattering analyses; the zeta potential is used to characterize the colloidal properties of the suspensions and atomic force microscopy for determining particle dimensions. The presence of the sulfate half-ester group decreases the rate of oxidation. However, the content of the sulfate half-ester groups decreases when degree of oxidation reaches approx. 50%. We demonstrate that the CNC surfaces are affected by the oxidation beyond the C2–C3 bond cleavage: insight into the kinetics of the oxidation process is a prerequisite for optimizing CNC oxidation.

Applications of Biocatalysts for Sustainable Oxidation of Phenolic Pollutants: A Review

Phenol and its derivatives are hazardous, teratogenic and mutagenic, and have gained significant attention in recent years due to their high toxicity even at low concentrations. Phenolic compounds appear in petroleum refinery wastewater from several sources, such as the neutralized spent caustic waste streams, the tank water drain, the desalter effluent and the production unit. Therefore, effective treatments of such wastewaters are crucial. Conventional techniques used to treat these wastewaters pose several drawbacks, such as incomplete or low efficient removal of phenols. Recently, biocatalysts have attracted much attention for the sustainable and effective removal of toxic chemicals like phenols from wastewaters. The advantages of biocatalytic processes over the conventional treatment methods are their ability to operate over a wide range of operating conditions, low consumption of oxidants, simpler process control, and no delays or shock loading effects associated with the start-up/shutdown of the plant. Among different biocatalysts, oxidoreductases (i.e., tyrosinase, laccase and horseradish peroxidase) are known as green catalysts with massive potentialities to sustainably tackle phenolic contaminants of high concerns. Such enzymes mainly catalyze the o-hydroxylation of a broad spectrum of environmentally related contaminants into their corresponding o-diphenols. This review covers the latest advancement regarding the exploitation of these enzymes for sustainable oxidation of phenolic compounds in wastewater, and suggests a way forward.

Research progress of non-cyanide gold leaching in gold mines

With the exhaustion of easy-to-treat gold ore resources, gold ores containing arsenic, carbon, high sulfur, and ultrafine particles have become the focus of gold mining. These difficult-to-treat gold ores have poor leaching effects through conventional cyanide leaching methods. The chemicals involved in the production process are highly toxic, which can endanger human health and seriously pollute the ecological environment. Some countries and regions have restricted or prohibited the use of cyanide to extract gold; besides, cyanide treatment contains copper, zinc, nickel, etc. When removing impurities from gold ores, these impurity metals will increase the consumption of cyanide and oxidant in the leaching system. At the same time, a film will be formed on the gold surface that hinders the leaching of gold in cyanide and reduces the leaching rate of gold. Gold-containing substances that are insoluble in the cyanide solution include antimony compounds, aurostibite, black bismuth gold ore, and gold-containing compounds formed during reduction roasting of lead, antimony, and arsenic minerals. Although these compounds are present in small quantities, they may account for a large proportion of the amount of gold lost during processing. Nevertheless, the cyanidation method is currently the main process for processing gold ores. Due to the existence of defects in the cyanidation method and the declining gold ore suitable for cyanide treatment, scholars from all over the world are studying alternatives for gold leaching to realize an efficient and environment-friendly recovery of gold in difficult-to-treat gold mines. This article summarized the methods of non-cyanide leaching of gold: thiosulfate method, glycine method, halide method, lime sulfur mixture method, iodination roasting process, biological oxidation thiourea leaching method, and non-aqueous gold leaching method. The gold leaching principles of seven non-cyanide gold leaching methods and the latest research progress in refractory gold mines were introduced. The development direction of non-cyanide leaching gold technology was prospected based on the problems of non-cyanide gold leaching methods such as expensive leaching agent, difficulty in recovering gold in leaching solution, complicated leaching system, unstable properties of leaching agent, and large consumption.

Application of solar-based oxidation to the management of empty pesticide container rinse water in Bolivia.

Background: The management of empty pesticide containers (EPC) in Bolivia has been recently promoted as a control strategy for dispersed pollution in surface and underground water bodies, as well as in soil. It comprises the rinsing and proper disposal or reuse of clean EPC. However, the rinsing transfers the hazard to water, which must be properly treated before being discharged. Methods: In this study, solar photo-Fenton at low Fe 2+ doses were tested at pilot plant scale in Cochabamba (Bolivia) for the removal of pesticides dimethoate and atrazine in their commercial form, spiked in river water. Results: The results demonstrated that solar photo-Fenton ([H 2O 2] 0 = 200 mg L -1) with Fe 2+ concentrations between 0.5 and 1.5 mg L -1 is an effective method to remove dimethoate and atrazine, at an initial concentration of 10 mg L -1 each. Efficiency increased when increasing Fe 2+ doses, achieving a removal over 99% of both pesticides after a solar irradiation period of 60 minutes (corresponding to an accumulated energy of 4.96 kJ L -1). Conclusions: The presence of high concentrations of natural components of river water, mainly organic and inorganic carbon species, would have contributed to hydroxyl radical scavenging, explaining, together with the low iron dose applied, the high energy (irradiation time) and high hydrogen peroxide concentration required to produce pesticide depletion. Additionally, the relatively low oxidant consumption and mineralization observed leave room for process optimization regarding oxidant and catalyst doses and warrant further studies on its coupling with biological or other post-treatments for the removal of transformation products.

Degradation of HCHs by thermally activated persulfate in soil system: Effect of temperature and oxidant concentration

Soils contaminated with hexachlorocyclohexanes (HCHs) are a legacy of the heavy use of lindane during the 20th century. This pesticide production generated large amounts of residues of other HCH isomers, which were habitually mismanaged. The sediments treated in this work (coming from an old lindane landfill) are an example of this environmental problem of global dimensions. The efficient remediation of these sediments, mainly contaminated with β-HCH (99 mg kg−1) and α-HCH (254 mg kg−1) isomers, is still a challenge. The thermal activation of persulfate (PS) required excessive reaction times, which could be reduced by optimizing the variables of the process. This study aims to explore the effect of using higher reaction temperatures (35, 45, and 55 ºC) and initial oxidant concentrations (10, 20, 40, 60, and 80 g L−1). Batch experiments (liquid/soil = 2/1, 100 rpm) were performed to evaluate the influence of these two variables in HCHs abatement, dechlorination degree, generation of intermediate compounds, and oxidant consumption. An increase in the reaction temperature accelerates the pollutant oxidation and dechlorination rate and decreases the concentration of chlorinated byproducts. The initial PS concentration also plays a crucial role in HCHs degradation. At selected operating conditions (55 ºC, PS = 80 g L−1), a conversion of HCHs around 83% was achieved, without chlorinated byproducts (chlorine balance ≈ 100%) at only 9 days of treatment. A plausible pathway for the degradation of HCHs-polluted soils by thermally activated PS has been proposed from the identified species, involving a scheme of series-parallel reactions.

Fluorine doped g-C3N4 coupled NiFe2O4 heterojunction: Consumption of H2O2 for production of hydroxyl radicals towards paracetamol degradation

Construction of visible-light-driven heterojunction photocatalyst with robust redox ability to degrade the organic pollutant is a great challenge in environmental remediation field. Herein, we have proposed the F (fluorine) doped carbon nitride (FCN) coupled NiFe2O4 (NFO) heterojunction for photo Fenton-like commercial paracetamol (PAM) drug degradation. Fluorine doping in g-C3N4 could enhance the light absorption ability and inhibit the charge recombination rate through intermediate band structure. The addition of NFO to FCN further reduces the charge recombination rate and leads to photon Fenton-like degradation. The enormous production of hydroxyl (OH•) radicals through photo-Fenton reaction can greatly improves the PAM degradation and exhibited the 71% of TOC removal efficiency. The reactive oxygen species for the photo Fenton-like reaction was determined by adding NBT (nitroblue tetrazolium), and TA (terephthalic acid) as a trapping reagent for O2− and OH• radicals respectively. High consumption of chemical oxidant (H2O2) also plays a vital role in OH• radical production and PAM degradation. The FCN coupled NFO photocatalyst with high activity and stability could acts as a promising material for environmental remediation application.

Characterization of marine dissolved organic matter and its effect on ozonation

As the marine industry develops, the importance of seawater treatment process is increasing. To treat seawater, oxidation processes have primarily been used, such as ballast water treatment systems, aquaculture farm operations, aquarium management, and seawater desalination. However, dissolved organic matter in seawater, whose characteristics vary spatially and seasonally, affects the efficiency of oxidation processes. Therefore, in this study, seawater samples were acquired from various locations in the Republic of Korea to understand the spatio-temporal patterns of marine dissolved organic matter. It was reported that the characterization of marine dissolved organic matter using liquid chromatography—organic carbon detector and excitation-emission matrix—parallel factor modeling. Furthermore, the effects of marine dissolved organic matter were evaluated on ozonation, an oxidation process. The results demonstrate that marine dissolved organic matter varies in its aquagenic, pedogenic, and intermediate characteristics based on region and season. These variations affect ozonation by influencing the consumption of oxidants (e.g., bromine). As a result, it was concluded that characterizing marine dissolved organic matter can help improve the effectiveness of oxidation processes, particularly ozonation.

Selective and Efficient Olefin Epoxidation by Robust Magnetic Mo Nanocatalysts

Iron oxide magnetic nanoparticles were synthesized with different sizes (11 and 30 nm). Subsequently they were shelled with a silica layer allowing grafting of an organic phosphine ligand that coordinated to the [MoI2(CO)3] organometallic core. The silica layer was prepared by the Stöber method using either mechanical (both 11 and 30 nm nanoparticles) or ultrasound (30 nm only) stirring. The latter nanoparticles once coated with silica were obtained with less aggregation, which was beneficial for the final material holding the organometallic moiety. The Mo loadings were found to be 0.20, 0.18, and 0.34 mmolMo·g−1 for MNP30-Si-phos-Mo,MNP11-Si-phos-Mo, and MNP30-Sius-phos-Mo, respectively, with the ligand-to-metal ratio reaching 4.6, 4.8, and 3.2, by the same order, confirming coordination of the Mo moieties to two phos ligands. Structural characterization obtained from powder X-ray diffraction (XRD), scanning electron microscopy (SEM)/ transmission electron microscopy (TEM) analysis, and Fourier-transform infrared (FTIR) spectroscopy data confirmed the successful synthesis of all nanomaterials. Olefin epoxidation of several substrates catalyzed by these organometallic nano-hybrid materials using tert-butyl hydroperoxide (tbhp) as oxidant, achieved very good results. Extensive testing of the catalysts showed that they are highly active, selective, recyclable, and efficient concerning oxidant consumption.

Post-treatment of real municipal wastewater effluents by means of granular activated carbon (GAC) based catalytic processes: A focus on abatement of pharmaceutically active compounds

Pharmaceutically active compounds (PhACs) widely present in urban wastewater effluents pose a threat to ecosystems in the receiving aquatic environment. In this work, efficiency of granular activated carbon (GAC) - based catalytic processes, namely catalytic wet peroxide oxidation (CWPO), peroxymonosulfate oxidation (PMS/GAC) and peroxydisulfate oxidation (PDS/GAC) at ambient temperature and pressure were studied for removal of 22 PhACs (ng L−1 level) that were present in secondary effluents of real urban wastewater. Concentrations of PhACs were measured using Ultra Performance Liquid Chromatography – Triple Quadrupole Mass Spectrometry (UPLC-QqQ-MS/MS). Catalytic experiments were conducted in discontinuous mode using up-flow fixed bed reactors with granular activated carbon (GAC) as a catalyst. The catalyst was characterized by means of N2 adsorption-desorption isotherm, mercury intrusion porosimetry (MIP), elemental analysis, X-ray fluorescence spectroscopy (WDXRF), X-ray diffraction (XRD), thermal gravimetry and differential temperature analyses coupled mass spectrometry (TGA-DTA-MS). Results indicate that the highest efficiency in terms of TOC removal was achieved during CWPO performed at optimal operational conditions (stoichiometric dose of H2O2; TOC removal ~ 82%) followed by PMS/GAC (initial PMS concentration 100 mg L−1; TOC removal ~73.7%) and PDS/GAC (initial PDS concentration 100 mg L−1; TOC removal ~ 67.9%) after 5 min of contact time. Full consumption of oxidants was observed in all cases for CWPO and PDS/GAC at contact times of 2.5 min, while for PMS/GAC it was 1.5 min. In general, for 18 out of 22 target PhACs, very high removal efficiencies (> 92%) were achieved in all tested processes (including adsorption) performed at optimal operational conditions during 5 min of contact time. However, moderate (40 – 70%) and poor (< 40%) removal efficiencies were achieved for salicylic acid, ofloxacin, norfloxacin and ciprofloxacin, which can be possibly attributed to insufficient contact time. Despite high efficiency of all studied processes for PhACs elimination from urban wastewater effluent, CWPO seems to be more promising for continuous operation.

Kinetics of Microcystin-LR Removal in a Real Lake Water by UV/H2O2 Treatment and Analysis of Specific Energy Consumption.

The hepatotoxin microcystin-LR (MC-LR) represents one of the most toxic cyanotoxins for human health. Considering its harmful effect, the World Health Organization recommended a limit in drinking water (DW) of 1 µg L−1. Due to the ineffectiveness of conventional treatments present in DW treatment plants against MC-LR, advanced oxidation processes (AOPs) are gaining interest due to the high redox potential of the OH• radicals. In this work UV/H2O2 was applied to a real lake water to remove MC-LR. The kinetics of the UV/H2O2 were compared with those of UV and H2O2 showing the following result: UV/H2O2 > UV > H2O2. Within the range of H2O2 tested (0–0.9 mM), the results showed that H2O2 concentration and the removal kinetics followed an increasing quadratic relation. By increasing the initial concentration of H2O2, the consumption of oxidant also increased but, in terms of MC-LR degraded for H2O2 dosed, the removal efficiency decreased. As the initial MC-LR initial concentration increased, the removal kinetics increased up to a limit concentration (80 µg L−1) in which the presence of high amounts of the toxin slowed down the process. Operating with UV fluence lower than 950 mJ cm−2, UV alone minimized the specific energy consumption required. UV/H2O2 (0.3 mM) and UV/H2O2 (0.9 mM) were the most advantageous combination when operating with UV fluence of 950–1400 mJ cm−2 and higher than 1400 mJ cm−2, respectively.

Magnetite/graphite carbon nitride composite for peroxymonosulfate non-radical activation

Magnetite-based catalysts are cost-effective and recyclable in water treatment processes. In this work, we constructed Fe3O4/g-C3N4 (FeOCN) catalyst by compounding g-C3N4 and Fe3O4. Based on characterization and experiments, the local positive and negative charges create active sites for catalyzing peroxymonosulfate (PMS) and bisphenol A (BPA) was confirmed. Through free radical quenching experiment, electron spin resonance spectroscopy, oxidant consumption and XPS, the mechanism of FeOCN-catalyzed PMS degradation of BPA was discussed. The electron transfer of surface-bound reactive complexes and 1O2 were proved to play a role in the system. FeOCN not only achieves a pseudo first-order rate constant 35.7 times higher than Fe3O4, but also imparts pH stability (3–11) and applicability in actual water substrates (tap water, lake water, groundwater). This work provides a new insight into the engineering design of magnetite in the water treatment process to effectively treat organically polluted water.

Hydrazone-derived copper(II) coordination polymer as a selective liquid-phase catalyst: Synthesis, crystal structure and performance towards benzyl alcohol oxidation

In this study, we report the synthesis and physicochemical characterization of a novel one-dimensional copper(II) coordination polymer ([Cu(L)2]n) based on 2-acetylfuranisonicotinichydrazone, as well as its catalytic activity in the liquid-phase oxidation of benzyl alcohol. Based on spectroscopic and single crystal X-ray diffraction crystallography, the Cu(II) ion is pentacoordinated, bonded to two anionic hydrazones through the N,O chelating sites, and to the N-pyridyl atom from a third ligand molecule, which provides the formation of a one-dimensional network. The coordination polymer was evaluated as homogeneous catalyst, attaining high selectivity (90.1 %) and yield (36.9 %) towards benzaldehyde under mild conditions (70 °C, 2.10 mol% and 1:1 substrate-to-oxidant molar ratio). The efficiency was attributed to the slow tuning of the catalyst’s solubility in the reaction medium during the oxidation process by commitment of the use of an adequate solvent (acetonitrile) for efficient consumption of oxidant (TBHP) and formation of benzaldehyde. Titration experiments with TBHP, as well as an inhibitory essay, have shown the possible involvement of radical and peroxo reactive pathways in the reaction mechanism. Altogether, the results demonstrates that [Cu(L)2]n is suitable for accessible and mild fine chemical processes, in alignment with the search of environmentally friendly applications for industrial purposes.

Thermodynamic Analysis of Zinc Sulfide Dissolution Stoichiometry in Sulfuric Acid Solution with Oxygen Participation

In this work, a thermodynamic study of zinc sulfide high temperature oxidative leaching was carried out. At the metals sulfides dissolution under oxidants action in acidic solutions several simultaneously proceeding reactions are possible. With the aim finding the proportion of potential reactions, a thermodynamic calculation was carried out using stoichiometric equations with equal oxidant consumption. Moreover, stoichiometric coefficients were chosen in such a way that reagents could exchange 1 mole of electric charge. Such an approach allows one to ensure a comparison of different oxidants’ usage effectiveness for sulfide leaching. Thermodynamic analysis results are in accordance with experimental data, which confirm that reactions with the formation of sulfur and sulfate-ions are uppermost at zinc sulfide dissolution in sulfuric acid solutions under oxygen action. Oxygen consumption and initial sulfuric acid concentration influence on proportion of this reactions and zinc equilibrium concentration in solution were investigated. Thermodynamic analysis showed that at insufficient acid concentration, which limits the maximum degree of zinc sulfide oxidation reaction advancements with sulfur formation, oxygen is consumed on oxidation reaction with the formation of sulfate-ions, which spend oxygen less effectively, due to four times smaller zinc dissolution. Thermodynamic calculations carried out allowed us to find out optimal proportions of oxygen consumption and initial sulfuric acid concentration, which provide achievement of a maximal zinc equilibrium concentration in solution at a higher effectiveness of oxidant consumption without labor-intensive experiments. At optimal acid consumption, a zinc equilibrium concentration is directly proportional to initial acid concentration. Directly proportional dependence of zinc cations’ formation on acid consumption was also detected at acid concentration optimal values.

Decomposition performance of hypochlorite on bead-type NiOx(OH)y catalyst: improving applicability of catalysts.

An easy-to-use, pollution-free and reusable beaded NiOx(OH)y catalyst for improving hypochlorite oxidation was prepared by impregnating the mixture of persulfate and alkali over alumina and then reduced it with Ni2+. The effects of catalyst preparation conditions and reaction parameters on NaClO conversion rate and Ni2+ dissolution rate were studied. Impregnating the γ-Al2O3 beads in PS/OH- mixed solution with 0.59 M PS and PS/OH- molar ratio of 1.1, and then reducing with 0.8 M Ni2+ solution is the best condition for preparing catalyst. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The best catalytic layer is characterized by high content of chemisorbed oxygen which can be converted into atomic oxygen. The hypochlorite conversion rate increased with the catalyst dosage and reuse times, and decreased with available chlorine, while pH of hypochlorite solution had little effect on the conversion rate. After running stably for 120 h in continuous flow test, the chemisorbed oxygen content in the optimal catalytic layer decreased slightly. Atomic oxygen plays an important role in the decolorization of dye solution by NaClO/NiOx(OH)y system. The oxidant consumption cost of this process is much cheaper than Fenton reagent. The prepared catalyst has great potential in hypochlorite decomposition and wastewater treatment.