Preparation of GO/COFs composites by interlayer-confined strategy for the adsorption of nitro aromatic pollutants.

With the continuous development of industrialization, the excessive emission of nitro aromatic with strong toxicity, high carcinogenicity and non-degradability has attracted great attention. How to efficiently remove nitro aromatic pollutants is an important research topic. In this work, graphene oxide/covalent organic frameworks (GO/COFs) composites were successfully synthesized via interlayer confinement strategy selecting GO, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTP) and 1,3,5-tri(4-aminophenyl)benzene (TPB) as raw materials. Due to high specific surface area, hierarchical porous structure and good thermal stability, GO/COFs were utilized to adsorb and remove nitro aromatic hydrocarbons in the water environment. The adsorption behavior of GO/COFs for o-nitrophenol, 1,3-dinitrobenzene and 2,4,6-trinitrophenol were further investigated. The GO/COFs composites showed the strongest adsorption capacity for 2,4,6-trinitrophenol, and the maximum adsorption capacity for 2,4,6-trinitrophenol, o-nitrophenol, and 1,3-dinitrobenzene were 438, 317, and 173 mg g-1, respectively. The experimental results indicated that the GO/COFs composites provided great adsorption capability for nitro aromatic pollutants and can be reused, rendering it an extremely potential adsorbent for organic pollutants.

Fabrication of magnetic polydopamine@naphthyl microporous organic network nanosphere for efficient extraction of hydroxylated polycyclic aromatic hydrocarbons and p-nitrophenol from wastewater samples.

Herein, we report the fabrication of a novel, well-defined core-double-shell-structured magnetic Fe3O4@polydopamine@naphthyl microporous organic network (MON), Fe3O4@PDA@NMON, for the efficient magnetic extraction of hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) and p-nitrophenol (p-Npn) from wastewater samples. The hierarchical nanospheres were designed and constructed with the Fe3O4 nanoparticle core, the inner shell of a polydopamine (PDA) layer, and the outer shell of a porous naphthyl MON (NMON) coating, allowing efficient and synergistic extraction of OH-PAHs and p-Npn via hydrophobic, hydrogen bonding, and π-π interactions. The Fe3O4@PDA@NMON nanospheres were well characterized and employed as an efficient sorbent for magnetic solid-phase extraction (MSPE) coupled with high performance liquid chromatography (HPLC) for analyzing of OH-PAHs and p-Npn. Under optimal conditions, the Fe3O4@PDA@NMON-based-MSPE-HPLC-UV method afforded wide linear range (0.18-500 µg L-1), low limits of detection (0.070 µg L-1 for p-Npn, 0.090 µg L-1 for 2-OH-Nap, 0.090 µg L-1 for 9-OH-Fluo and 0.055 µg L-1 for 9-OH-Phe, respectively), large enrichment factors (92.6-98.4), good precisions (intra-day and inter-day relative standard deviations (RSDs); <6.4%, n=6) and less consumption of the adsorbent. Furthermore, trace OH-PAHs and p-Npn with concentrations of 0.29-0.80 µg L-1 were successfully detected in various wastewater samples. Fe3O4@PDA@NMON also functioned as a good adsorbent to enrich a wide scope of trace contaminants containing hydrogen bonding sites and aromatic structures, highlighting the potential of functional MONs in sample pretreatment.

Electrospun metal-organic frameworks with polyacrylonitrile as precursors to hierarchical porous carbon and composite nanofibers for adsorption and catalysis.

A facile and effective method has been developed to prepare hierarchical porous carbon nanofibers (PCNFs), carbon nanofibers supported nickel nanoparticles (PCNFs-Ni) and carbon nanofibers encapsulating gold nanoparticles (PCNFs-Au). PCNFs or PCNFs-Au were obtained by embedding metal-organic frameworks (e.g. ZIF-8 or ZIF-8-Au) into polyacrylonitrile via electrospinning and subsequent carbonization. In addition, PCNFs-Ni were obtained by impregnating PAN/ZIF-8 nanofibers in Ni(NO3)2·6H2O followed by carbonization. Both PCNF and PCNF-Ni exhibited excellent adsorption activities for methylene blue (MB) and congo red (CR). Especially, PCNF-Ni could be removed and separated via a magnet. PCNFs-Au showed excellent catalytic properties in the reduction reaction of 4-nitrophenol (4-NP).

A versatile ratiometric electrochemical sensing platform based on N-Mo2C for detection of m-nitrophenol.

M-nitrophenol (m-NP) is a high priority environmental pollutant and poses a series of threats on human health. Accurate and rapid detection of m-NP in practical samples is very important as this is the key prerequisite for its effective monitoring. Eelectrochemical sensor, though long serving as highly sensitive and fast analytical tool, suffers from the bottleneck problems like low specificity, poor reproducibility, susceptibility to internal and external disturbances, etc. Herein, we developed a ratiometric electrochemical sensor (R-ECS) for m-NP detection, in which nitrogen-doped Mo2C (N-Mo2C) was deployed as the sensing agent and methylene blue (MB) as the internal reference. Full characterization of N-Mo2C was carried out in the aspects of morphology, composition, chemical bonds and electrochemical behavior, and the sensing performance of the easy-to-operate R-ECS was evaluated. Complete separation of the oxidation peaks of m-NP and MB was achieved using the MB/N-Mo2C composite modified electrode and their ratiometric signals were adopted for quantification of m-NP. The linear relation between the electrical signal and the concentration of m-NP is in the range of 1-1500 µM, with the detection limit of 0.256 µM (S/N = 3). The sensor was applied to measure m-NP in real samples from tap water and river. Experimental results demonstrate that it exhibits decent repeatability, reproducibility, stability and selectivity, which proves its great practical potential as an analytical detector.

Biosynthesis of gold nanoparticles using fungus Trichoderma sp. WL-Go and their catalysis in degradation of aromatic pollutants.

An efficient green method of gold nanoparticles (AuNPs) biosynthesis was achieved by cell-free extracts of fungus Trichoderma sp. WL-Go. Based on UV-Vis spectra, AuNPs biosynthesised by cell-free extracts with 90 mg/l protein exhibited a characteristic absorption band at 556 nm and was stable for 7 days. Transmission electron microscopy images revealed that the as-synthesised AuNPs were spherical and pseudo-spherical, and the average size was calculated to be 9.8 nm with a size range of 1-24 nm. The AuNPs illustrated their good catalytic activities for reduction of nitro-aromatics (2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitroaniline, 3-nitroaniline) with catalytic rate constants of 7.4 × 10-3 s-1, 10.3 × 10-3 s-1, 4.9 × 10-3 s-1, 5.8 × 10-3 s-1, 15.0 × 10-3 s-1, respectively. Meanwhile, the AuNPs also showed excellent catalytic performance in decolourisation of azo dyes with decolourisation efficiency from 82.2 to 97.5%. This study provided a green gentle method for AuNPs synthesis as well as exhibiting efficient catalytic capability for degradation of aromatic pollutants.

Chitosan-coated polyurethane sponge supported metal nanoparticles for catalytic reduction of organic pollutants.

In this research work, polyurethane sponge (PUS) is used as a readily removable substrate for the synthesis of different nanoparticles on the surface and its use in reducing toxic dyes. An aqueous solution of 0.5 wt% chitosan (CH) was coated on PUS to prepare an ionophilic CH-PUS material. The CH-PUS pieces were then kept in 0.05 M concentration of four different salt solutions. After absorbing the metal ions for a 4 h time period, the CH-PUS pieces were treated with 0.2 M NaBH4 solution to convert the adsorbed ions to the analogous metal nanoparticles. The bare PUS, CH-PUS and M/CH-PUS were analyzed by various spectroscopic techniques. After catalytic testing of different M/CH-PUS under similar conditions using a model reaction of 4-nitrophenol (4-NP) reduction by NaBH4, we found that Cu/CH-PUS outperformed among the other M/CH-PUS. The Cu/CH-PUS catalyzed the 4-NP reduction with the fastest reaction rate constant of 0.7923 min-1. We also tested with different factors affecting the reaction rate constant such as different weights of catalyst, various concentrations of 4-NP and NaBH4. Lastly, after testing Cu/CH-PUS catalyst for the reduction of different dyes, its high performance was observed for the congo red dye.

A facile synthesis of CuAg nanoparticles on highly porous ZnO/carbon black-cellulose acetate sheets for nitroarene and azo dyes reduction/degradation.

A facile and highly porous heterostructure nanocomposite was designed for the support of zero-valent metal nanoparticles. This nanocomposite comprising of ZnO/carbon black (ZnO/CB) embedded in cellulose acetate polymer (CA), named as ZCA sheet, supported the metallic Cu, Ag and bimetallic CuAg nanoparticles (NPs). The ZnO/CB was incorporated to CA polymer host molecule in 3, 4 and 5 wt% and are designated as ZCA-3, ZCA-4 and ZCA-5. The catalytic tunability was evaluated for CuAg/ZCA-5 by adjusting the concentration of Cu and Ag ions in different molar ratio. Therefore, the CuAg/ZCA-5 was further selected for the removal of eight model pollutants comprising of o-nitrophenol (ONP), m-nitrophenol (MNP), p-nitrophenol (PNP), 2,6-dinitrophenol (DNP), methyl orange (MO), congo red (CR), methylene blue (MB) and rhodamine B (RB). The Kapp value for PNP was 1.9 × 10-1 min-1 and 9.0 × 10-2 min-1 for MO. Among the various nitrophenols, the rate of reaction with CuAg/ZCA-5 followed the ordered as PNP ˃ ONP ˃ MNP ˃ DNP, while methyl orange (MO) is degraded faster as compared to other dyes. The morphology, shape, elemental analysis, functional groups and peak crystallinity were scrutinized through FESEM, EDS, ATR-FTIR and XRD respectively.

Simultaneous p-nitrophenol and nitrogen removal in PNP wastewater treatment: Comparison of two integrated membrane-aerated bioreactor systems.

The chemical p-nitrophenol (PNP) is a priority pollutant, and PNP wastewater is highly toxic and resistant to biodegradation. The traditional physical and chemical methods (adsorption, extraction, and oxidation) for treating PNP wastewater have the disadvantages of complicated processes, high costs and secondary pollution generation. In this study, two integrated membrane-aerated bioreactor systems (RA and RB) with anoxic and aerated zones were constructed to enhance PNP biodegradation. The results showed that a helical silicone rubber membrane module displayed a high oxygen supply rate under a low membrane aeration pressure, and the hydraulic flow state of the reactor approached ideal mixing. At an influent PNP concentration of 500 mg/L, the average removal rates of PNP, chemical oxygen demand (COD) and total nitrogen (TN) reached 95.86%, 89.77%, and 94.81%, respectively, for RA and 89.48%, 74.26% and 64.78%, respectively, for RB, indicating efficient simultaneous PNP and nitrogen removal. Compared with that of RB, the pre-anoxic zone in RA not only performed detoxification pretreatment but also enhanced PNP degradation and denitrification effects, which relieved the biological treatment burden of the subsequent aerated zone. Based on these comprehensive analyses of reactor performance, the hydroquinone pathway might be the main route in the aerobic degradation of PNP.

Bioaugmented soil aquifer treatment for P-nitrophenol removal in wastewater unique for cold regions.

P-nitrophenol (PNP) is a toxic and recalcitrant organic pollutant and a usual intermediate in the production of fine chemicals, which has posed a significant threat to subsurface environment safety. Soil aquifer treatment (SAT) is a promising method to remove and remediate contamination in vadose zone with low cost and high efficiency. However, there are still research gaps for the treatment of recalcitrant contaminants by SAT in cold regions, such as un-robust indigenous microbes and low temperature constraint in vadose zone. The bioaugmentation technology was first introduced into SAT in order to enhance the removal ability of PNP by SAT operated in cold regions in this study. A high-efficiency PNP-degrading bacterium was successfully isolated, which can efficiently degrade PNP below 200 mg L-1 with a degradation rate above 99% at 15 °C close to the real subsurface temperature in cold regions, and added into SAT for bioaugmentation. The feasibility of bioaugmented SAT and associated PNP removal process were investigated by laboratory sand columns, along with effects of the SAT operative parameters (namely PNP loading concentration, flow rate and soil saturation level of SAT). Within the range of PNP loading stresses tested (1-200 mg L-1), PNP removal efficiency was optimal at constant flow rate of 219 mL d-1 in unsaturated operating condition of SAT under 15 °C among all the investigated experimental conditions. Longer hydraulic residence time increased the PNP removal rate, although the accumulated mass removed reduced and the removal efficiencies remained constant in unsaturated operating condition of SAT. It is found from the comparison between the PNP removals via both unsaturated and saturated columns that slight difference only in the removal rate of PNP was observed and the highly efficient bioaugmented SAT can completely degrade PNP of 10 mg L-1 within 5 wetting/drying cycles under both scenarios.

Two-dimensional mesoporous ZnCo2O4 nanosheets as a novel electrocatalyst for detection of o-nitrophenol and p-nitrophenol.

Novel mesoporous ZnCo2O4 (meso-ZnCo2O4) nanosheets were synthesized by a simple hydrothermal method for detection of o-nitrophenol (ONP) and p-nitrophenol (PNP). The resultant meso-ZnCo2O4 nanosheets possess more catalytic active sites than other structures, which enhance the catalysis properties for the electrochemical detection of nitrophenol. This sensor exhibits a wide linear detection range (1-4000 and 1-4000 µM) and high sensitivity (0.256 and 0.318 µA µM-1 cm-2), as well as low detection limit (0.3 and 0.3 µM), for ONP and PNP, respectively. In addition, the fabricated sensor reveals excellent reproducibility, stability and selectivity.

Performance of cellulose acetate-ferric oxide nanocomposite supported metal catalysts toward the reduction of environmental pollutants.

Water contamination by toxic compounds has become one of the most serious problems worldwide. Catalytic reduction using metal nanoparticles offer opportunities for environmental benefits. In this study, cellulose acetate-ferric oxide nanocomposite (CA/Fe2O3) was prepared and used as support for metal nanoparticles. After adsorption of Ag, Cu or Ni ions from aqueous solutions, metal ions associated with CA/Fe2O3 were treated with sodium borohydride to prepare Ag, Cu and Ni nanoparticles loaded CA/Fe2O3. The CA/Fe2O3 supported Ag, Cu or Ni nanoparticles was evaluated as a catalyst for pollutants degradation. Silver nanoparticles (Ag@CA/Fe2O3) exhibit remarkable decomposition for methyl orange dye and p-nitrophenol in short time. The rate constant for methyl orange and p-nitrophenol were 8.58×10-3 and 4.77×10-3s-1, respectively. Besides the good catalytic activities of Ag@CA/Fe2O3, the catalyst could be easily recovered from the reaction medium by pulling the catalyst after completion of the reduction reaction. The recovered catalyst can be recycled several times if their exposure time to air was minimal.

Premagnetization enhancing the reactivity of Fe0/(passivated Fe0) system for high concentration p-nitrophenol removal in aqueous solution.

In order to strengthen the treatment efficiency of Fe0 based system for high concentration wastewater treatment, Fe0 particles were passivated by concentrated nitric acid, and a premagnetization Fe0/(passivated Fe0) system was setup for high concentration p-nitrophenol (PNP) removal in this study. The significant parameters of this system were optimized. Under the optimal conditions, the premagnetization Fe0/(passivated Fe0) system could obtain high kobs value for PNP removal (0.100 min-1) and COD removal (15.0% after 60 min) for high concentration PNP (500 mg/L) treatment. In addition, five control experiments were set up to confirm the advantage of the premagnetization Fe0/(passivated Fe0) system. The results suggest that passivated Fe0 particles could be stimulated better than Fe0 particles by premagnetization process, and the premagnetization Fe0/(passivated Fe0) systems is much superior to the other five control systems. Furthermore, the pathway for PNP destruction treated by 6 different systems was also proposed according to intermediates determination by High Performance Liquid Chromatography (HPLC) and UV-vis spectrum, and the carbon mass balance was demonstrated according to the COD and HPLC analyses. Finally, the characteristics of (premagnetization) Fe0 and passivated Fe0 was detected by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and vibrating sample magnetometer (VSM), and the mechanism of premagnetization effectively enhancing the reactivity of Fe0/(passivated Fe0) system (better than that of Fe0 system) was proposed. Consequently, the premagnetization for reactivity improvement of Fe0/(passivated Fe0) system is a promising technology to enhance the efficiency of this system for high concentration wastewater treatment.

Enhancing the efficiency of zero valent iron by electrolysis: Performance and reaction mechanism.

Electrolysis was applied to enhance the efficiency of micron-size zero valent iron (mFe0) and thereby promote p-nitrophenol (PNP) removal. The rate of PNP removal by mFe0 with electrolysis was determined in cylindrical electrolysis reactor that employed annular aluminum plate cathode as a function of experimental factors, including initial pH, mFe0 dosage and current density. The rate constants of PNP removal by Ele-mFe0 were 1.72-144.50-fold greater than those by pristine mFe0 under various tested conditions. The electrolysis-induced improvement could be primarily ascribed to stimulated mFe0 corrosion, as evidenced by Fe2+ release. The application of electrolysis could extend the working pH range of mFe0 from 3.0 to 6.0 to 3.0-10.0 for PNP removal. Additionally, intermediates analysis and scavengers experiments unraveled the reduction capacity of mFe0 was accelerated in the presence of electrolysis instead of oxidation. Moreover, the electrolysis effect could also delay passivation of mFe0 under acidic condition, as evidenced by SEM-EDS, XRD, and XPS analysis after long-term operation. This is mainly due to increased electromigration meaning that iron corrosion products (iron hydroxides and oxides) are not primarily formed in the vicinity of the mFe0 or at its surface. In the presence of electrolysis, the effect of electric field significantly promoted the efficiency of electromigration, thereby enhanced mFe0 corrosion and eventually accelerated the PNP removal rates.

Anticancer, antibacterial and pollutant degradation potential of silver nanoparticles from Hyphaene thebaica.

We present here the biosynthesis of AgNps from the aqueous extract of H. thebaica fruit, and monitored through UV-Vis spectrophotometer. The functional group were characterized through ATR-FTIR spectroscopy, the particle size, morphologies and elemental composition of the nanoparticles were investigated by using TEM, FESEM and EDS respectively. The anti-proliferation activity of the synthesized AgNps was carried out using MTT assay on human prostate (PC3), breast (MCF7) and liver (HepG2) cancer cell lines. The anti-proliferation assay showed that the AgNps were able to inhibit the proliferation of the cancer cell lines in a dose depending manner. The effect was found more pronounced on prostate (IC50 2.6 mg/mL) followed by breast (IC50 4.8 mg/mL) and then liver cancer cell lines (IC50 6.8 mg/mL). The prepared AgNps were found to inhibit 99% growth of both E. coli and S. aureus after 24 h of incubation. The nanoparticles were used for the degradation of 4-nitrophenol (4-NP) and Congo red dyes (CR), which efficiently degrade CR, but make complex formation with 4-NP. Therefore, the AgNps synthesized from the aqueous fruit extract of H. thebaica have potential application in pharmacology and waste water treatment.

Thin layer chitosan-coated cellulose filter paper as substrate for immobilization of catalytic cobalt nanoparticles.

A facile approach utilizing synthesis of cobalt nanoparticles in green polymers of chitosan (CS) coating layer on high surface area cellulose microfibers of filter paper (CFP) is described for the catalytic reduction of nitrophenol and an organic dye using NaBH4. Simple steps of CFP coating with 1wt% CS aqueous solution followed by Co2+ ions adsorption from 0.2M CoCl2 aqueous solution were carried out to prepare pre-catalytic strips. The Co2+ loaded pre-catalytic strips of CS-CFP were treated with 0.19M NaBH4 aqueous solution to convert the ions into nanoparticles. Successful Co nanoparticles formation was assessed by various characterization techniques of FESEM, EDX and XRD analyzes. TGA analyses were carried out on CFP, CS-CFP, and Co-CS-CFP for the determination of the amount of Co particles formed on the CS-FP, and to track their thermal properties. Furthermore, we demonstrated that the Co-CS-CFP showed an excellent catalytic activity and reusability in the reduction reactions a nitroaromatic compound of 2,6-dintirophenol (2,6-DNP) and brilliant cresyl blue (BCB) dye by NaBH4. The Co-CS-CFP catalyzed the reduction reactions of 2,6-DNP and BCB by NaBH4 with psuedo-first order rate constants of 0.0451 and 0.1987min-1, respectively.

Preparation of high-quality activated carbon from polyethyleneterephthalate (PET) bottle waste. Its use in the removal of pollutants in aqueous solution.

A waste-treats-waste approach has been used for the removal of two common pollutants, namely p-nitrophenol and/or Fe(III) from aqueous solution. Polyethyleneterephthalate (PET) from bottle waste has been used as the precursor for the preparation of activated carbons (ACs) by physical activation with steam and chemical activation with potassium hydroxide under controlled heating conditions and atmospheres. The resulting ACs were characterized in terms of chemical composition, porous texture and surface chemistry, and morphology. Selected ACs were tested as adsorbents for the removal of the aforementioned pollutants in aqueous solution. For comparison purposes, a commercial AC was also used. In general, the yield of the process of preparation of ACs is lower than 10% with steam and between 24.62 and 32.07% with potassium hydroxide. ACs possess a very high carbon content and a very low ash content. The BET surface areas reach 1235 m(2) g(-1) with steam and 1002 m(2) g(-1) with potassium hydroxide at most. Also, the degrees of development of micro- and mesoporosity are markedly larger with steam. Conversely, the development of macroporosity is much larger with potassium hydroxide. The PET-derived ACs exhibit a better adsorption behavior towards p-nitrophenol than the commercial AC, both in terms of adsorption rate and adsorption capacity. On the contrary, the commercial AC acts as a better adsorbent of Fe(III) ions. As compared to separately, the simultaneous presence of both solutes in the adsorptive solution scarcely affects the adsorption process except for equilibrium for Fe(III).

Comprehensive comparison of bacterial communities in a membrane-free bioelectrochemical system for removing different mononitrophenols from wastewater.

Membrane-free bioelectrochemical systems (MFBESs) have been developed for the degradation of nitro-aromatic contaminants, but the microbial communities that are involved have not been comprehensively investigated. In this study, the microbial communities were evaluated and compared for treating different structures of nitrophenols (NPs), i.e., o-nitrophenol (ONP), m-nitrophenol (MNP) and p-nitrophenol (PNP), in the MFBES. The results demonstrated that NPs reduction in the MFBES decreased in efficiency in the following order: ONP>MNP>PNP. Illumina MiSeq sequencing results showed that richness and diversity of bacterial species in the anodic and cathodic communities decreased when fed different NPs. Though remarkable differences in community composition were found between anodic and cathodic biofilms in the MFBES, three core genera-Treponema, Desulfovibrio and Geobacter-were dominant in the anodic or cathodic biofilm, regardless of various NPs. Other functional genera in the anodic or cathodic biofilm were selectively enriched in the MFBES treating the three NPs with different structures.

Layer-by-layer assembly of zeolite imidazolate framework-8 as coating material for capillary electrochromatography.

In this work, open-tubular capillary column coated with zeolite imidazolate framework-8 (ZIF-8) nanocrystals was prepared by a layer-by-layer method. The coating was formed by growing ZIF-8 nanocrystals on either bare fused silica capillary wall or the capillary column premodified with amino groups. The shape and the thickness of the coating formed by using these two methods were almost the same. However, the coverage of the ZIF-8 crystals on the bare fused silica capillary wall was higher than that on the capillary column premodified with amino groups. The ZIF-8 coated capillary column was evaluated for open-tubular capillary electrochromatography. The effect of pH value, buffer concentration, and applied voltage on the separation of phenols was investigated. Good separation of nine phenolic isomers was achieved because of the strong interaction between unsaturated Zn sites and phenols. The column performance for o-nitrophenol was as high as 208 860 plates m(-1) . The run-to-run, day-to-day, and column-to-column reproducibility of retention time and resolution for p-nitrophenol and o-nitrophenol were very good with RSDs of less than 6.5%.

Fully solar-driven thermo- and electrochemistry for advanced oxidation processes (STEP-AOPs) of 2-nitrophenol wastewater.

The STEP (Solar Thermal Electrochemical Process) for Advanced Oxidation Processes (AOPs, combined to STEP-AOPs), fully driven by solar energy without the input of any other forms of energy and chemicals, is introduced and demonstrated from the theory to experiments. Exemplified by the persistent organic pollutant 2-nitrophenol in water, the fundamental model and practical system are exhibited for the STEP-AOPs to efficiently transform 2-nitrophenol into carbon dioxide, water, and the other substances. The results show that the STEP-AOPs system performs more effectively than classical AOPs in terms of the thermodynamics and kinetics of pollutant oxidation. Due to the combination of solar thermochemical reactions with electrochemistry, the STEP-AOPs system allows the requisite electrolysis voltage of 2-nitrophenol to be experimentally decreased from 1.00 V to 0.84 V, and the response current increases from 18 mA to 40 mA. STEP-AOPs also greatly improve the kinetics of the oxidation at 30 °C and 80 °C. As a result, the removal rate of 2-nitrophenol after 1 h increased from 19.50% at 30 °C to 32.70% at 80 °C at constant 1.90 V. Mechanistic analysis reveals that the oxidation pathway is favorably changed because of thermal effects. The tracking of the reaction displayed that benzenediol and hydroquinone are initial products, with maleic acid and formic acid as sequential carboxylic acid products, and carbon dioxide as the final product. The theory and experiments on STEP-AOPs system exemplified by the oxidation of 2-nitrophenol provide a broad basis for extension of the STEP and AOPs for rapid and efficient treatment of organic wastewater.

Formation of 2-nitrophenol from salicylaldehyde as a suitable test for low peroxynitrite fluxes.

There has been some dispute regarding reaction products formed at physiological peroxynitrite fluxes in the nanomolar range with phenolic molecules, when used to predict the behavior of protein-bound aromatic amino acids like tyrosine. Previous data showed that at nanomolar fluxes of peroxynitrite, nitration of these phenolic compounds was outcompeted by dimerization (e.g. biphenols or dityrosine). Using 3-morpholino sydnonimine (Sin-1), we created low fluxes of peroxynitrite in our reaction set-up to demonstrate that salicylaldehyde displays unique features in the detection of physiological fluxes of peroxynitrite, yielding detectable nitration but only minor dimerization products. By means of HPLC analysis and detection at 380nm we could identify the expected nitration products 3- and 5-nitrosalicylaldehyde, but also novel nitrated products. Using mass spectrometry, we also identified 2-nitrophenol and a not fully characterized nitrated dimerization product. The formation of 2-nitrophenol could proceed either by primary generation of a phenoxy radical, followed by addition of the NO2-radical to the various resonance structures, or by addition of the peroxynitrite anion to the polarized carbonyl group with subsequent fragmentation of the adduct (as seen with carbon dioxide). Interestingly, we observed almost no 3- and 5-nitrosalicylic acid products and only minor dimerization reaction. Our results disagree with the previous general assumption that nitration of low molecular weight phenolic compounds is always outcompeted by dimerization at nanomolar peroxynitrite fluxes and highlight unique features of salicylaldehyde as a probe for physiological concentrations of peroxynitrite.