P-nitrophenol Removal Efficiency Research Articles

Magnetite nanoparticles decorated on cellulose aerogel for p-nitrophenol Fenton degradation: Effects of the active phase loading, cross-linker agent and preparation method

Magnetite nanoparticles (Fe3O4 NPs) are among the most effective Fenton-Like heterogeneous catalysts for degrading environmental contaminants. However, Fe3O4 NPs aggregate easily and have poor dispersion stability because of their magnetic properties, which seriously decrease their catalytic efficiency. In this study, a novel environmentally friendly method for synthesising Fe3O4@CA was proposed. Fe3O4 NPs were immobilized on the 3D cellulose aerogels (CAs) in order to augment the degradation efficiency of p-nitrophenol (PNP) treatment and make the separation of the catalyst accessible by vacuum filtration method. Besides, CAs were fabricated from a cellulose source extracted from water hyacinth by using different cross-linking agents, such as kymene (KM) and polyvinyl alcohol–glutaraldehyde system (PVA–GA), and other drying methods, including vacuum thermal drying and freeze drying, were evaluated in the synthesis process. As-synthesized samples were analysed by various methods, including Powder X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis and Brunauer–Emmett–Teller. Then, using ultraviolet–visible spectroscopy, the difference in the degradability of PNP of the obtained material samples was also investigated to determine their potential applications. Results highlighted that the Fe3O4-3@CA-KF catalyst with an Fe3O4 loading of 0.40 g/gCA used KM as a cross-linker and the freeze-drying method demonstrated the highest PNP removal efficiency (92.5 %) in all Fe3O4@CA samples with a H2O2 content of 5 g/L. The degradation kinetics and well-fitted pseudo-first-order model were investigated. Notably, after five successive PNP degradation experiments, this catalyst retained ∼80 % of the ability to degrade PNP, indicating its outstanding reusability. In environmental remediation, this study provides valuable insights into the development of simply separated and high-efficiency catalysts for heterogeneous catalytic reactions.

Electrochemical surface plasmon resonance approach to probe redox interactions between microbial extracellular polymeric substances and p-nitrophenol

Microbial extracellular polymeric substances with redox functional groups play a crucial role in the bio-conversion of pollutants, which can affect their reactivity toward diverse pollutants. However, the redox interactions between microbial EPS and pollutants have not addressed in depth due to the absence of essential analytical methodologies. In this study, we have developed an electrochemical-surface plasmon resonance (EC-SPR) system to investigate the interactions between EPS and p-nitrophenol (PNP) by simultaneously monitoring the electrochemical reaction and the binding kinetics. Moreover, in vitro PNP degradation experiments were performed in the presence of EPS across varying redox states to provide further verification of PNP reduction by EPS. The results indicated that direct electrochemical treatment successfully converted raw EPS (EPSraw) into reductive EPS (EPSred) and oxidized EPS (EPSox), respectively. The EC-SPR system served as a powerful tool for probing redox interactions between EPS at distinct redox states and PNP. The binding affinity of EPS to PNP was related to the redox states of EPS, following the order of EPSred > EPSraw > EPSox. EPS exhibited the capability to reduce PNP to p-aminophenol by donating electrons, and the reductive process highly depended on the redox states of EPS, primarily determined by their electron donating capacity. Importantly, direct electrochemical reduction treatment of EPS leads to a substantial improvement in the PNP removal efficiency from 33.8% (EPSraw) to 56.9% (EPSred). This work contributes to a comprehensive understanding of the critical role of EPS redox property in the conversion of refractory pollutants in aquatic environments.

Co-removal of P-nitrophenol and nitrate in sulfur-based autotrophic and methanol-fed heterotrophic denitrification bioreactors

P-nitrophenol (PNP) can co-occur with nitrate (NO3-) in industrial and municipal wastewater due to effluent discharges from industry and agricultural activities. In this study, the simultaneous removal of PNP and NO3- was investigated under autotrophic and heterotrophic denitrifying conditions in two bioreactor columns at laboratory scale. Autotrophic denitrification with elemental sulfur showed efficient elimination of both PNP (85 % on average for 5–50 mg/L) and NO3- (99 % on average) even at feed PNP concentration of 50 mg/L. In contrast, the heterotrophic column showed significantly lower PNP removal (53 % on average for 5–50 mg/L) despite denitrification efficiency being ≥ 95 %. ORP was identified as a possible control parameter to modulate PNP removal efficiency. The autotrophic column showed better resiliency than the heterotrophic one under intermittent feeding of 50 mg/L of PNP. Absorbance spectra and HPLC results revealed no accumulation of PNP by-products, i.e., aminophenol, in the autotrophic column during transient feeding conditions.

Characterization and mechanism of p-nitrophenol removal based on modified nanoscale zero-valent iron electrocoagulation

p-Nitrophenol (PNP) is a toxic chemical and is difficult to degrade naturally when it enters the environment. It is of great importance to develop methods to remove PNP efficiently and safely. Electrocoagulation has been widely used for the removal of PNP, but challenges remain in the improvement of anode materials and solid-liquid separation of PNP-containing precipitates. In this work, the characteristics and mechanism of activated biochar (ABC) and sulfide dual-modified nanoscale zero-valent iron (nZVI) electrocoagulation anode for the removal of PNP were systematically investigated. The synergistic effect of magnetic iron oxide generated by zero-valent iron oxidation and electrochemical oxidation technique was used to rapidly reduce the PNP concentration for water purification. The results showed that the modified nZVI anode had higher electrocoagulation activity than the iron sheet anode, and the S-nZNI/ABC anode had the highest PNP removal efficiency. The main component of the precipitate after the reaction was Fe3O4, which facilitated the magnetic solid-liquid separation of the precipitate and scum. The seed germination test confirmed that the electrocoagulation material synthesized in this work had almost no adverse effects on the ecological environment. The electrocoagulation process had good degradation performance for PNP, which could significantly attenuate the ecotoxicity of PNP in the aquatic environment and thus improve the water quality. It is expected that this work may provide design references and ideas for the efficient degradation of PNP and the application of electrocoagulation.

Heterogeneous Fenton treatment of shale gas fracturing flow-back wastewater by spherical Fe/Al2O3 catalyst.

In this work, efficient Fenton strategy have been proposed for degradation of shale gas fracturing flow-back wastewater using the spherical Fe/Al2O3 supported catalyst. Prior to actual fracturing fluid treatment, the typical model wastewaters such as p-nitrophenol and polyacrylamide were employed to evaluate the catalytic properties of prepared catalyst, and then Fenton treatment of the shale gas fracturing flow-back wastewater was performed on the self-assembled catalytic degradation reactor for continuous flow purification. Results showed that under the conditions of 0.25 mol L-1 impregnating concentration, pH 4, 50 g L-1 catalyst and 0.75 mL L-1 30% H2O2, the removal efficiency of p-nitrophenol and polyacrylamide reached 74% and 61%, respectively, while the COD removal of fracturing flow-back fluid was approximately 48% with the residual 88 mg L-1 COD, meeting the emission standards of the integrated wastewater discharge standard (GB 8978-1996, COD < 100 mg L-1). This work offers new alternatives for Fenton treatment of real wastewater by efficient and low-cost supported catalysts.

Bifunctional erdite rods as an effective flocculant and catalyst in electro-Fenton systems

Erdite rods were massively produced via a one-step alkaline heating route with the complete recycling of waste waterwork sludge. The sludge was a mixture of Fe, Mn, Al, and Si, but only Fe-bearing substances were converted as erdite rods. The erdite rods had 100 ​nm diameter and 1-5 ​μm length, and was hydrolysed as Fe-SH-rich flocs in wastewater. Its hydrolysis became slow in the presence of electric field but accelerated by adding PMS. p-Nitrophenol was targeted as organic pollutant to determine the rods performance. The removal efficiency of p-nitrophenol was 7.4% by adding erdite rods, but up to 44.6% with the addition of erdite/PMS, and then dramatically increased to 98.7% in the electro-PMS/erdite system. Given that the free Fe was less than 30 ​mg/L, the surface Fe of Fe-SH-rich flocs predominated the PMS activation, in which the surface Fe enriched in electronic field and then was involved in the redox reaction of PMS and then reduced by the adjacent S on flocs. This enabled the recycling of Fe3+/Fe2+ to activate PMS at high level. Thus, the erdite rods showed high p-nitrophenol removal efficiency in the electro-Fenton system in comparison with the other reported reagents, e.g. ferrous sulphate, ferbam, pyrite and FeS.

Ultrasonic-electrodeposition construction of high hydrophobic Ce-PDMS-PbO2/SS electrode for p-nitrophenol degradation: Catalytic, kinetics and mechanism

In this work, a novel hydrophobic microsphere Ce-PDMS-PbO2 structure on stainless steel (SS) was prepared via ultrasonic-electrodeposition as an efficient anodic electrocatalyst for p-nitrophenol (PNP) degradation. Compared to PbO2/SS, such Ce-PDMS-PbO2/SS electrode exhibits obviously lower activation energy (19.20 kJ mol−1) and charge transfer resistance (3.268 Ω cm−2), tolerable stability, higher exchange current density (1.171 ×10−5 A cm−2) and electrochemical active area (202.0 cm2). The as-synthesized Ce-PDMS-PbO2/SS anode achieved drastically enhanced PNP removal efficiency of 96.9% in 120 min, and the degradation reaction-order was calculated to be 0.9123 conformed to the quasi-first-order reaction kinetics. The GC-MS results reveal the possible PNP degradation pathway under the action of both anodic and cathodic reactions. Furthermore, the DFT calculation results show that Ce doping can decrease the activation energy barrier of ·OH and promote the ·OH generation. Overall, this work offers a new strategy and comprehension to construct a high-efficiency electrode for PNP pollutants degradation.

Removal of p-nitrophenol by double-modified nanoscale zero-valent iron with biochar and sulfide: Key factors and mechanisms

In this study, the mechanisms and key factors of p-nitrophenol (PNP) removal by biochar (BC) and sulfide double-modified nanoscale zero-valent iron (nZVI) were systematically investigated. The results showed that the residence time of the hydrothermal carbonization of waste bamboo chopsticks was the key factor affecting the removal of PNP by nZVI/BC. The biochar derived from waste bamboo chopsticks prepared at a hydrothermal temperature of 240 °C for 1 h was the most suitable nZVI loading material. The hydrophobicity of the biochar had a greater impact on S-nZVI/BC. Biochar effectively alleviated the agglomeration of nZVI and formed a miniature galvanic cell with nZVI to promote its corrosion. The effective reducing agents in the S-nZVI/BC system were Fe0, Fe2+, S2−, and S22−, and the system had stronger reducibility then nZVI. The reaction rate of S-nZVI/BC for PNP removal was 2.6 times higher than that of nZVI. In addition, the double modification of nZNI reduced the energy barrier of the PNP removal reaction and alleviated the surface passivation of nZVI. The apparent activation energy of the reaction under anaerobic conditions after sulfidation treatment was reduced by 23.7 %, while the PNP removal efficiency increased by 8 % under aerobic conditions. Density Function Theory (DFT) calculations revealed that PNP was more easily adsorbed and participated in the reaction on the surface of the sulfide shell layer than oxidized shell layer. This work confirms that biochar loading and surface sulfidation can enhance the reactivity and stability of nZVI.

Synergistic degradation of aqueous p-nitrophenol using DBD plasma combined with ZnO photocatalyst

In this study a dielectric barrier discharge non-thermal plasma (DBD-NTP) reactor was combined with ZnO nanoparticles to degrade p-nitrophenol (PNP) in aqueous solution. When the plasma process was combined with ZnO nanoparticles an obvious improvement was obtained in PNP removal efficiency. this was seemingly due to activation of ZnO photocatalysts under the UV light produced in discharge region. The results showed that addition of the optimum amount of ZnO nanoparticles (250 mg/L) to the plasma reactor could increase the removal efficiency from 49 % to 91 %, whereas the UV/ZnO photocatalytic process alone only lead to 12 % PNP removal. This is indicative of the synergistic enhancement of PNP degradation efficiency in the combined NTP-ZnO process rather than simply an additive effect. The effects of intial solution pH, applied voltage, and initial PNP concentration were also investigated on the sole NTP and NTP-ZnO processes in terms of removal efficiency. Alkaline solution conditions, and lower initial PNP concentration favored both processes, while the applied voltage of 13 kV yielded the optimum PNP removal. Furthermore, higher total organic carbon (TOC) removal and higher kinetic constant of PNP degradation was achieved in the plasma system coupled with ZnO photocatalysis. Energy consumption analysis revealed that the NTP-ZnO process is 4.25 times more energy efficient than the sole plasma process which could be a major step towards industrial utilization of plasma treatment technologies.

Treatment of organic wastewater by ozone in a continuous rotating solid foam stirrer tank

The work herein employed a novel rotating solid foam stirrer tank (RSFST) under continuous operation in attempt to intensify ozone-liquid mass transfer rate and possibly enhance treatment of organic wastewater. P-nitrophenol (PNP) and acid red B (ARB) were separately used to simulate phenolic and dye wastewater. Results show that the removal efficiency of PNP and ARB dye increased with increasing rotational speed and gas flow rate but decreased with increasing liquid flow rate and initial wastewater concentration. The highest removal efficiency of PNP and ARB was attained at pH of 11 and 7, respectively. Ozone utilization efficiency increased with increasing stirring speed, liquid flow rate, initial wastewater concentration and pH but decreased with increasing gas flow rate. The treatment efficiency of organic wastewater in the RSFST reactor is superior to that of many other reactors (rotating packed bed and bubble column, etc.). Correlations to predict the removal efficiency of the organics were developed and the deviation between the experimental and predicted values is within 15%, indicating that the correlations can be used to predict the removal efficiency of PNP and ARB by ozone in RSFST. The study provides a scientific reference for development of a new high-efficiency ozone oxidation reactor.

Preparation of coal fly ash-based Fenton-like catalyst and its application for the treatment of organic wastewater under microwave assistance

In order to realize the high value-added reuse of coal fly ash (CFA), a reusable CFA catalyst (AFA) for a Fenton-like process conducted under microwave (MW) assistance was prepared by H2SO4 impregnation. The optimal AFA preparation conditions included an impregnation time of 60 min, H2SO4 dosage of 0.5 mol/L, impregnation temperature of 303 K, and solid–liquid ratio of 1 g:5 mL. In addition, several AFA critical parameters such as specific surface area, pore size distribution, particle size distribution, surface morphology, relative content, chemical states of the elements on the AFA surface, mass fractions of various AFA oxides, crystal composition, surface chemical bonds, and coordination structure of Si were determined. The dynamic treatment conditions of organic wastewater were optimised using a continuous wastewater treatment system with MW assistance, and the removal efficiency of p-nitrophenol (PNP) exceeded 90% at a hydraulic retention time of 40 min. The AFA was successfully reused three times while retaining a PNP removal efficiency of 90%. The relationship between the PNP removal rate and the utilised treatment conditions was −d[PNP]dt=0.32⋅[H2O2]0.374⋅[AFA]0.337⋅[H+]0.445⋅[PNP]0.475. Furthermore, the AFA surface played the main role and ·OH was the most reactive oxidative radical. Hence, real coking wastewater can be effectively treated by the AFA-catalysed Fenton-like process under MW assistance.

Efficient removal of p-nitrophenol from water using montmorillonite clay: insights into the adsorption mechanism, process optimization, and regeneration.

The present research highlights the use of a montmorillonite clay to remove p-nitrophenol (PNP) from aqueous solution. The montmorillonite clay was characterized using powder X-ray diffraction, Fourier-transformed infrared spectroscopy, scanning electron microscopy, X-ray fluorescence, Brunauer-Emmett-Teller analyses, and zero point charge in order to establish the adsorption behavior-properties relationship. The physiochemical parameters like pH, initial PNP concentration, and adsorbent dose as well as their binary interaction effects on the PNP adsorption yield were statistically optimized using response surface methodology. As a result, 99.5% removal of PNP was obtained under the optimal conditions of pH 2, adsorbent dose of 2 g/l, and PNP concentration of 20 mg/l. The interaction between adsorbent dose and initial concentration was the most influencing interaction on the PNP removal efficiency. The mass transfer of PNP at the solution/adsorbent interface was described using pseudo-first-order and intraparticle diffusion. Langmuir isotherm well fitted the experimental equilibrium data with a satisfactory maximum adsorption capacity of 122.09 mg/g. The PNP adsorption process was thermodynamically spontaneous and endothermic. The regeneration study showed that the montmorillonite clay exhibited an excellent recycling capability. Overall, the montmorillonite clay is very attractive as an efficient, low-cost, eco-friendly, and recyclable adsorbent for the remediation of hazardous phenolic compounds in industrial effluents.

Surfactant-Modified Clay Sorbents for the Removal of p-nitrophenol

AbstractOrganic pollutants are widespread and a known problem for the environment. p-nitrophenol (PNP) is one such pollutant found in effluents from various industries involved with pesticides, pharmaceuticals, petrochemicals, plastic, paper, and other materials. The objective of this research was to prepare and test organically modified clays using four different surfactants and to evaluate the removal efficiency of PNP from aqueous solutions. Organically modified clays have attracted great interest due to their wide applications in industry and environmental protection as sorbents for organic pollutants. Two natural smectite-dominated clay types from outcrops in Latvia and Lithuania as well as industrially manufactured montmorillonite (Mt) clay were modified using different nonionic (4-methylmorpholine N-oxide (NMO) and dimethyldodecylamine N-oxide (DDAO)) and cationic (benzyltrimethyl ammonium chloride (BTMAC) and dodecyltrimethyl ammonium chloride (DTAC)) surfactants. Modified clay materials were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer-Emmett-Teller method (BET) for surface area analysis. Sorption of PNP was investigated under various conditions, e.g. surfactant loading, initial PNP concentration, contact time, and pH. The novelty of the present study was to prepare innovative organo-sorbents based on manufactured as well as natural clay samples using cationic surfactants and nonconventional nonionic surfactants as modifiers. The sorption data combined with FTIR and XRD supplementary results suggests that nonionic organo-clay (Mt-DDAO_2) is the most effective sorbent and may serve as a low-toxicity immobilizer of pollutants such as phenols.

A new MOFs/polymer hybrid membrane: MIL-68(Al)/PVDF, fabrication and application in high-efficient removal of p-nitrophenol and methylene blue

MOFs/polymer hybrid membranes combine the special surface activity of MOFs and the excellent carries nature of porous polymer and thus exhibit unexpected adsorption/separation performances in the solid-phase extraction. In this paper, a new kind of MOFs/polymer composite membrane, MIL-68(Al)/PVDF have been fabricated for the first time through blending the MIL-68(Al) nanoparticles and polyvinylidene fluoride (PVDF) casting solution and following the lyotropic phase transition. Some means such as SEM, XRD and FT-IR are used to character the structure of these hybrid membranes. The membrane performances including the hydrophilic/hydrophobic properties, membrane porosity and membrane water flux are also measured. The effects of doping amount of MIL-68(Al) on the structure and performances of MIL-68(Al)/PVDF hybrid membranes are discussed. Two persistent organic pollutants: p-nitrophenol (PNP) and methylene blue (MB) are chosen as main adsorption objects to evaluate the adsorption activity of MIL-68(Al)/PVDF hybrid membranes. The influences of various conditions on the adsorption activities are investigated in detail and the optimum adsorption conditions are determined. All the MIL-68(Al)/PVDF hybrid membranes exhibit enhanced adsorption capacity compared to pristine PVDF, and the adsorption activities of hybrid membranes are promoted continually with the increasing doping contents of MIL-68(Al). The adsorption thermodynamics analysis indicates that the adsorption process is mainly characterized by Langmuir monolayer adsorption and chemical adsorption. The coordination bonding formed between NO2 of PNP and Al(III) of MIL-68(Al), and the acid-base interaction between the sulfur of MB and Al(III) of MIL-68(Al) may be responsible to the highest removal efficiency of PNP and MB. The good dynamics adsorption and regeneration performances indicate the prospect applications of these MOFs/PVDF hybrid membranes in the separation of organic contaminants from industrial waste water.

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.

Synthesis of Chitosan-Functionalized Fibrous Membrane for Immobilization of Horseradish Peroxidase: Interfacial Property and Application for Catalytic Oxidation of P-Nitrophenol

A hydrophilic fibrous membrane consisting of a network of a non-crystalline hydrophobic polymer and an in situ crosslinked hydrophilic chitosan polymer is studied. This chitosan-functionalized membrane can be employed as a support for immobilization of horseradish peroxidases (HRPs). The immobilized HRPs (mass loading ~110 mg /g) show high stabilities over a wide pH range of 4~10 and temperature range of 25~60°C. In addition, the immobilized HRPs can function as a recyclable biocatalyst for catalytic oxidation of p-nitrophenol (PNP). After 10 cycles, the PNP removal efficiency is 70 percent. The results demonstrate that the chitosan-functionalized fibrous membrane is a promising support for immobilization of enzymes and has applications related to enzyme catalysis.

Microwave-assisted synthesis of ZnNiAl-layered double hydroxides with calcination treatment for enhanced PNP photo-degradation under visible-light irradiation

In this paper, ZnNiAl-layered double hydroxide (LDH) photocatalysts were successfully prepared using a facile and timesaving microwave-assisted method. ZnNiAl-layered double oxides (LDOs) were then achieved from ZnNiAl-LDHs photocatalyst with calcination treatment. As a control, the corresponding photocatalysts were synthesized using a traditional hydrothermal method. A set of characterization technologies including XRD, SEM, FT-IR, and N2 adsorption was carried out to investigate the physical and chemical properties of the prepared photocatalysts. The photocatalytic activities were evaluated by the degradation of p-nitrophenol (PNP) under visible-light irradiation. Moreover, the influences of calcination temperature, photocatalyst dosage, and initial PNP concentration were also explored in this system. The results indicated that the sample transformed from LDH to LDO after 700 ○C calcination treatment and the prepared LDO showed an outstanding photocatalytic activity. When the photocatalyst dosage was 1.0 g·L−1 and initial PNP concentration was 10 mg·L−1, PNP removal efficiency was as high as 93.0% within 180 min under visible-light irradiation. After six cycles, the newly designed photocatalyst showed a good stability and reusability. This study shares a new preparation method for ZnNiAl-LDO as a novel photocatalyst with high efficiency for wastewater treatment.

Removal and Extraction of Para-Nitrophenol from Aqueous Samples Using Graphene Magnetic Nanocomposite

Graphene magnetic nanocomposite was synthesized and characterized for surface morphology, functional groups and thermal stability using scanning electron microscopy, Fourier transformed infrared spectrometry and thermogravimetric analysis. The composite was investigated for the extraction and removal of p-nitrophenol from aqueous samples. Different experimental factors such as pH, composite dose, time, temperature and concentration of p-nitrophenol were studied for the removal. At pH 4, p-nitrophenol removal efficiency was high and then decreased with increase in pH up to 10. The removal of p-nitrophenol was high with 60 min time and the % sorption remained constant up to 90 min. Experimental data of kinetic models were explained best by the pseudo-second-order kinetic model with sorption capacity and correlation coefficient values of 45.87 mg/g and 0.9998, respectively. The isotherm data followed Langmuir isotherm with correlation coefficient of 0.9903 and sorption capacity $$(\hbox {Q}_{{{\circ }}})$$ of 500 mg/g. The sorption of p-nitrophenol was found exothermic in nature and physisorption process involved in the sorption of p-nitrophenol on graphene magnetic nanocomposite. Electron donor–acceptor and hydrogen-bonding interactions were the mechanism involved in sorption. The results revealed that graphene magnetic nanocomposite has faster rate of removal of p-nitrophenol and can be used as a sorbent.

PH-dependent degradation of p-nitrophenol by sulfidated nanoscale zerovalent iron under aerobic or anoxic conditions

Sulfidated nanoscale zerovalent iron (S-NZVI) is attracting considerable attention due to its easy production and high reactivity to pollutants. We studied the reactivity of optimized S-NZVI (Fe/S molar ratio 6.9), comparing with pristine nanoscale zerovalent iron (NZVI), at various pH solutions (6.77⿿9.11) towards p-nitrophenol (PNP) under aerobic and anoxic conditions. Studies showed that the optimized extent of sulfidation could utterly enhance PNP degradation compared to NZVI. Batch experiments indicated that in anoxic S-NZVI systems the degradation rate constant increased with increasing pH up to 7.60, and then declined. However, in aerobic S-NZVI, and in anoxic or aerobic NZVI systems, it decreased as pH increased. It was manifested that anoxic S-NZVI systems preferred to weaker alkaline solutions, whereas aerobic S-NZVI systems performed better in acidic solutions. The highest TOC removal efficiency of PNP (17.59%) was achieved in the aerobic S-NZVI system at pH 6.77, revealing that oxygen improved the degradation of PNP by excessive amounts of hydroxyl radicals in slightly acidic conditions, and the TOC removal efficiency was supposed to be further improved in moderate acidic solutions. Acetic acid, a nontoxic ring opening by-product, confirms that the S-NZVI system could be a promising process for industrial wastewater containing sulfide ions.

Nitrophenols removal from aqueous medium using Fe-nano mesoporous zeolite

In this study, Fe-nano zeolite was applied to the removal of ortho, meta and para-nitrophenols to evaluate its potential applications as an effective adsorbent. Scanning electron microscopy, Fourier-transformed infrared spectroscopy, and gas adsorption analysis were used to compare the advanced properties of Fe-nano zeolite with those of commercial activated carbon (AC). The Fe-nano zeolite with a greatly improved surface area was particularly effective in the removal of the nitrophenols. The maximum adsorption capacity of m-, o- and p-nitrophenol were 168.7, 193.9 and 223.1mg/g, respectively. These adsorbents were applied to the remediation of wastewater containing high p-nitrophenol concentration of 380mg/L. The results revealed 92.8% removal efficiency of p-nitrophenol from wastewater by Fe-nano zeolite, which is much higher than those AC (56.5%). The regeneration characteristics of the p-nitrophenol-loaded adsorbent were analyzed. Even after 15 adsorption-desorption cycles, the removal efficiencies of p-nitrophenol by Fe-nano zeolite and AC were 78.6 and 57.9%, respectively. The required adsorption cost for the treatment of 1000kg wastewater containing 380mg/L of p-nitrophenol using Fe-nano zeolite was 67.6% lower than that using AC. Based on these results, Fe-nano zeolite can be used as economic and effective adsorbent for removal of nitrophenols from wastewater.