Treatment Of Organic Pollutants Research Articles

Removal of PFASs from water by carbon-based composite photocatalysis with adsorption and catalytic properties: A review.

Per- and polyfluoroalkyl substances (PFASs) are a class of persistent organic pollutants widely distributed in aquatic environments. The adsorption and photocatalytic methods have been widely used to remove PFASs in water because of their respective advantages. Still, they have apparent defects when used alone. Therefore, the adsorption and photocatalytic technologies are combined through suitable preparation methods, and the excellent properties of the two are used to synergize the treatment of organic pollutants. This strategy of "concentrating" pollutants and then degrading them in a centralized manner plays an essential role in removing trace PFASs. Nevertheless, a review focusing on this kind of adsorption photocatalyst system is lacking. This review will fill this gap and provide a reference for developing a carbon-based composite photocatalyst. Firstly, different carbon-based composite photocatalysts are reviewed in detail, focusing on the differences in various composite materials' excellent adsorption and catalytic properties. Secondly, the factors influencing the removal effect of carbon-based composite photocatalysts are discussed. Thirdly, the removal mechanism of carbon-based composite photocatalysts is summarized in detail. The removal process involves two steps: adsorption and photodegradation. The adsorption process involves multiple cooperative adsorption mechanisms, and photocatalytic degradation includes oxidative and reductive degradation. Fourthly, the comparison of adsorption-photocatalysis with common treatment techniques (including removal rate, range of adaptation, cost, and the possibility of expanding application) is summarized. Finally, the prospects of carbon-based composite photocatalysts for repairing PFASs are given by evaluating the performance of different composites.

Review of Advanced Oxidation Processes Based on Peracetic Acid for Organic Pollutants

In recent years, the removal of organic pollutants from water and wastewater has attracted more attention to different advanced oxidation processes (AOPs). There has been increasing interest in using peroxyacetic acid (PAA), an emerging oxidant with low or no toxic by-products, yet the promotion and application are limited by unclear activation mechanisms and complex preparation processes. This paper synthesized the related research results reported on the removal of organic pollutants by PAA-based AOPs. Based on the research of others, this paper not only introduced the preparation method and characteristics of PAA but also summarized the mechanism and reactivity of PAA activated by the free radical pathway and discussed the main influencing factors. Furthermore, the principle and application of the newly discovered methods of non-radical activation of PAA in recent years were also reviewed for the first time. Finally, the shortcomings and development of PAA-based AOPs were discussed and prospected. This review provides a reference for the development of activated PAA technology that can be practically applied to the treatment of organic pollutants in water.

Simultaneous activation of KHSO5 and BuOOH by iron octacarboxyphthalocyanine loaded on fly ash microspheres to boost pollutant degradation

Utilization of fly ash (FA) wastes as the carriers of catalysts for the environmental application is an economic and practical strategy for their low cost, easy accessibility and thermal stability. However, most catalysts immobilized on fly ash were metal or metal oxides, some potential catalysts such as metal phthalocyanine complexes have not been reported upon their heterogeneous catalysis with FA as the carriers. In this paper, highly active iron octacarboxyphthalocyanine were immobilized onto the bird nest-like surfaces of fly ash microspheres after NaOH activation. It is noted that the FeOCPc@FA composites with only 2 wt.% exhibited the high catalytic efficiency in the organic dye degradation. The high concentration of 30 mg/L rhodamine B and methylene blue could be fast decolorized in the presence of FeOCPc@FA–2 % and KHSO5. Moreover, the ultrafast decolorization of these dyes could be observed in the catalytic system composed of FeOCPc@FA–2 %, KHSO5 and BuOOH (tert-butyl hydroperoxide). Simultaneous activation of KHSO5 and BuOOH could be realized in our designed catalytic system. Based on the structural characterizations of composites and active species generated during the catalytic processes, the probable generation pathway of metal–oxygen active species and various radicals were analyzed to explicate the catalytic mechanism. Our investigation provides a high efficiency, low cost and environmentally friendly strategy for advanced oxidation treatment of organic pollutants.

Utilization of a biosurfactant foam/nanoparticle mixture for treatment of oil pollutants in soil.

Oil contamination has become a primary environmental concern due to increased exploration, production, and use. When oil enters the soil, it may attach or adsorb to soil particles and stay in the soil for an extended period, contaminating the soil and surrounding areas. Nanoparticles have been widely used for the treatment of organic pollutants in the soil. Surfactant foam has effectively been employed to remediate various soil contaminants or recover oil compounds. In this research, a mixture of biosurfactant foam/nanoparticle was utilized for remediation of oil-contaminated soil. The results demonstrated that the biosurfactant/nanoparticle mixture and nitrogen gas formed high-quality and stable foams. The foam stability depended on the foam quality, biosurfactant concentration, and nanoparticle dosage. The pressure gradient change in the soil column relied on the flowrate (N2 gas + surfactant/nanoparticle mixture), foam quality, and biosurfactant concentration. The optimal conditions to obtain good quality and stable foams and high oil removal efficiency involved 1 vol% rhamnolipid, 1 wt% nanoparticle, and 1 mL/min flowrate. Biosurfactant foam/nanoparticle mixture was effectively used to remediate oil-contaminated soil, whereas the highest treatment efficiency was 67%, 59%, and 52% for rhamnolipid biosurfactant foam/nanoparticle, rhamnolipid biosurfactant/nanoparticle, and only rhamnolipid biosurfactant, respectively. The oil removal productivity decreased with the increase of flowrate due to the shorter contact time between the foam mixture and oil droplets. The breakthrough curves of oil pollutants in the soil column also suggested that the foam mixture's maximum oil treatment efficiency was higher than biosurfactant/nanoparticle suspension and only biosurfactant.

Establishment of electrochemical treatment method to dye wastewater and its application to real samples

It is of great significance to study the treatment of organic dye pollution. In this work, a method of electrochemical treatment for reactive blue 19 dye (RB19) wastewater system was established, and it was applied to the actual dye wastewater treatment. The effects of applied voltage, electrolyte concentration, electrode spacing, and initial concentration on the removal effect of RB19 have been studied in detail. The results show that the removal rate of RB19 can reach 82.6% and the chemical oxygen demand (CODcr) removal rate is 54.3% under optimal conditions. The removal of RB19 in the system is mainly the oxidation of hydroxyl free radicals. The possible degradation pathway is inferred by ion chromatography: hydroxyl free radicals attack the chromophoric group of RB19 to make it fall off, and then decompose it into ring-opening. The product is finally oxidized to CO2 and water. The kinetic fitting is in accordance with the zero-order reaction kinetics. At the same time, using the established electrochemical system to treat the actual dye wastewater has also achieved good results. After 3 hours of treatment, the CODcr removal rate of the raw water is 44.8%, and the CODcr removal of the effluent can reach 89.5%. The degradation process conforms to the zero-order reaction kinetics. The result is consistent with the electrochemical treatment of RB19.

Metal-organic frameworks-derived CoFeN-NC materials with the enhanced catalytic activity and selectivity for the degradation of organic dyes via adsorption and heterogeneous photo-Fenton

Nanoscale iron-based materials are widely used as photocatalytic materials for catalytic oxidative degradation of organic dyes in water. Here, a series of MOFs derived nitrogen doped cobalt iron bimetallic carbon composite nanomaterials (CoxFe1-xN-NCs) were prepared by self-assembly and annealing treatment, and their application in the removal of organic dyes in water was investigated by the synergistic effect of adsorption and photo-Fenton. The study found that the Co0.8Fe0.2N-NC exhibit superior catalytic performance for different types of organic dyes. For example, when the concentration of MB was 40 mg L-1, the degradation rate constant was 3.88 × 10-2 min−1, which were 2.9 and 25.2 times the corresponding values of the Fenton-like and photocatalytic system, respectively. Meanwhile, compared with azo dyes Methyl Orange and Congo Red (MO and CR), Co0.8Fe0.2N-NC has obvious selective catalysis for non-azo dyes Methylene Blue, Malachite Green, Rhodamine B and Neutral Red (MB, MG, RhB and NR). Moreover, the reaction of cobalt iron active centers with hydrogen peroxide (H2O2) further promotes the generation of active substances (·OH, ·O2– and h+), speeding up the degradation of organic dyes. These results suggest that the synergistic effect of adsorption and photo-Fenton may provide new clues for the treatment of organic pollutants in wastewater.

Optimization of Conditions for Removal Phenolic Compounds from Water by a Graphene Oxide Aerogel

AbstractIn this study, graphene oxide (GO) was prepared from graphite by improved Hummers’ method. Graphene oxide aerogel (GOA) was synthesized via the ice segregation induced self‐assembly method. Various modern analytical methods were utilized to characterize GOA. The results revealed the aerogel structure with a pore size of 100–150 μm, a specific surface area of 515.21 m2/g, and a pore volume of 2.08–2.16 cm3/g. The synthesized GOA was applied as an adsorbent for the removal of phenol (PN) and bisphenol A (BPA) with a maximum adsorption capacity of 117.65 and 70.17 mg/g, respectively. Response surface methodology involving a rotating central composite design was applied to investigate simultaneously the effects of adsorption variables including adsorption time, pH, and initial concentration on the removal efficiency of GOA for PN or BPA. The results showed that the optimal adsorption efficiency for PN was 92.15 % with an adsorption time of 208.52 min, a pH of 6.08, and an initial PN concentration of 30 mg/L. Regarding BPA, the optimal adsorption efficiency was 95.27 % with an adsorption time of 352.79 min, a pH of 4.91, and an initial BPA concentration of 20 mg/L. The adsorption of both PN and BPA onto GOA was appropriate with the Langmuir model, in which the maximum adsorption capacity of GOA for PN and BPA was 117.65 and 70.175 mg/g, respectively. The results confirmed that the adsorption of PN and BPA onto GOA was monolayer adsorption on a homogeneous surface. The adsorption mechanism of GOA for PN or BPA depended mainly on the electrostatic interaction and hydrogen bonding between −OH of PN, BPA, and oxygen‐containing functional groups of GOA. Besides, π‐π interaction between carbon rings of GOA and PN or BPA also contributed to the enhancement of adsorption performance. The results showed that GOA exhibited potential application in the treatment of organic pollutants. Besides, the evaluation of the morphology of the GOA and the simultaneous effects of different factors can contribute to the advancement of graphene‐based materials and the improvement of wastewater treatment.

One-step construction of Ti-In bimetallic MOFs to improve synergistic effect of adsorption and photocatalytic degradation of bisphenol A

The key to efficient treatment of organic pollutants in water is to improve their mass transfer efficiency and reaction efficiency. Herein, a one-step construction of new metal-organic frameworks (MOFs) using 4, 4′, 4″, 4″-(pyrene-1, 3, 6, 8-tetrayl) tetra-benzoic acid as a photosensitizer ligand and Ti-In as bimetallic centers has been constructed. The results exhibited that increased specific surface area was obtained by Ti-In-MOF(1:1), which improved the adsorption performance of 50 ppm bisphenol A to 38% and facilitated it complete degradation upon light irradiation in 20 min, being much faster than that of single In/Ti-MOFs. For Ti-In-MOF(1:1), the In-MOF parts enhanced the adsorption capability, meanwhile the Ti-MOF parts based on infinite Ti-O chains realized the effective separation of photogenerated carriers. A synergistic role of adsorption and degradation achieved rapid mass transfer and excellent catalytic degradation performance. This investigation will provide a novel MOF construction strategy for efficient catalytic application in environmental pollutants.

Role of extremophilic Bacillus cereus KH1 and its lipopeptide in treatment of organic pollutant in wastewater.

An effective biosurfactant producer and extremophiles bacteria, Bacillus cereus KH1, was isolated from textile effluent and the biosurfactant was produced using molasses as the sole carbon source. Growth parameters such as pH, temperature, salinity and concentration of molasses were optimised for decolourising the textile effluent with 24-h incubation. The biosurfactant property of B. cereus KH1 was evaluated based on haemolytic activity, oil displacement technique, drop-collapsing test and emulsification index. The results of the produced biosurfactant showed a positive reaction in haemolytic activity, oil displacement technique, drop-collapsing test and exhibiting a 67% emulsification index. The cell-free broth was stable in 40°C pH 7, 7% salinity and 7% molasses. Thin-Layer Chromatography and Fourier Transform Infrared Spectroscopy analysis revealed that the biosurfactant was a lipopeptide with a yield 2.98gL-1. These findings proved the synergistic action of B. cereus KH1 with lipopeptide biosurfactant may accelerated the decolourisation efficiency to 87%.

CdS Coated Mn Doped ZnO Nanospheres as Textile Catalyst: Fabrication, Physicochemical Techniques and Dye Removal Under Natural Light

ZnO as a promising photocatalyst has gained much attention for the removal of organic pollutants from water. However, the main drawbacks of the relatively low photocatalytic activity and high recombination rate of photo excited electronhole pairs, restrict its potential applications. Promoting the spatial separation of photo excited charge carriers is of paramount signi? cance for photocatalysis, because the dierence in the band positions make the potential gradient at the composite boundary. In this work, our aim is to enhance the photocatalytic efficiency of CdS coated Mn doped ZnO nanospheres under solar light irradiation. Objectives in this work are, to fabricate the CdS coated Mn doped ZnO nanospheres by a simple ethanolic dispersion method, and its applied for testing the photocatalytic activity of methylene blue (MB) dye. The fabricated binary composites were analyzed with different physicochemical techniques like PXRD, SEM with EDX, UV-DRS, PL and TEM. The photocatalytic degradation results have revealed that, the CdS coated Mn doped ZnO nanospheres exhibits admirable activity toward the photocatalytic degradation of the MB. The remarkably enhanced photocatalytic activity of CdS coated Mn doped ZnO nanospheres can be interpreted in terms of lots of active sites, which efficiently separate the photo generated electron and holes. A plausible mechanism is also elucidated via active species trapping experiments with various scavengers, which indicating that the photo generated O2 -and. OH radicals play a crucial role in photo degradation reactions under visible light irradiation. This work suggests that, the rational design and construction of heterostructures is powerful for developing highly efficient, and reusable visible-light photocatalysts for environmental purification and energy conversion. The enhanced photo degradation activity indicates the potential of the nanocomposite for the treatment of organic pollutants from the textile wastewater.

CdS Coated Mn Doped ZnO Nanospheres as Textile Catalyst: Fabrication, Physicochemical Techniques and Dye Removal Under Natural Light

ZnO as a promising photocatalyst has gained much attention for the removal of organic pollutants from water. However, the main drawbacks of the relatively low photocatalytic activity and high recombination rate of photo excited electronhole pairs, restrict its potential applications. Promoting the spatial separation of photo excited charge carriers is of paramount signi? cance for photocatalysis, because the dierence in the band positions make the potential gradient at the composite boundary. In this work, our aim is to enhance the photocatalytic efficiency of CdS coated Mn doped ZnO nanospheres under solar light irradiation. Objectives in this work are, to fabricate the CdS coated Mn doped ZnO nanospheres by a simple ethanolic dispersion method, and its applied for testing the photocatalytic activity of methylene blue (MB) dye. The fabricated binary composites were analyzed with different physicochemical techniques like PXRD, SEM with EDX, UV-DRS, PL and TEM. The photocatalytic degradation results have revealed that, the CdS coated Mn doped ZnO nanospheres exhibits admirable activity toward the photocatalytic degradation of the MB. The remarkably enhanced photocatalytic activity of CdS coated Mn doped ZnO nanospheres can be interpreted in terms of lots of active sites, which efficiently separate the photo generated electron and holes. A plausible mechanism is also elucidated via active species trapping experiments with various scavengers, which indicating that the photo generated O2 -and. OH radicals play a crucial role in photo degradation reactions under visible light irradiation. This work suggests that, the rational design and construction of heterostructures is powerful for developing highly efficient, and reusable visible-light photocatalysts for environmental purification and energy conversion. The enhanced photo degradation activity indicates the potential of the nanocomposite for the treatment of organic pollutants from the textile wastewater.

Magnetic porous carbon composites for rapid and highly efficient degradation of organic pollutants in water

A magnetic porous carbon composite (MPC) was prepared from metal−organic frameworks (MOFs) by the one-step calcination method. The MPC was characterized by SEM, TEM, TG, DTG, Raman and XPS. The adsorption and degradation performance of MPC towards four organic dyes were investigated. The maximum adsorption amount of magenta on MPC was 191.94 mg g -1 at 25 °C. Furthermore, the MPC showed remarkable stability for it can be recycled 5 times through the facile magnetic separation without obvious loss of activity. The degradation efficiency of MPC toward four kinds of organic pollutants was nearly 100% within 36 ​min, which was much higher than that previously reported. • Magnetic Porous Carbon Composites is prepared by one step carbonization with excellent adsorption and catalytic degradation performance. • Maximum adsorption capacity of magenta on MPCs is 191.94 ​mg ​g −1 and nearly 100% degradation efficiency within 36 ​min. • Ultra-fine nanocrystalline Fe 3 O 4 nanoparticles embedded in the octahedral structure, are favor of removal and degradation of organic dye pollutants. • Carbon layer in MPCs is beneficial to avoid secondary pollution in degradation and contribute the stability and recyclability of MPCs. • MPCs possesses potential green and effective application of organic pollutants treatment in complex matrix.

Mechanism and efficiency research of P- and N-codoped graphene for enhanced paracetamol electrocatalytic degradation.

Electrocatalytic oxidation is an effective technology for treatment of refractory organic pollutants, and its performance strongly depends on anode materials. Among all anode materials, graphene (GN) owns the advantages of high stability and lack of secondary pollution. The catalytic performance of GN can be further improved through heteroatom doping. Here, P/N-codoped graphene (PN-GN) materials were optimized and used as an anode material for 4-acetamidophenol (APAP) electrocatalytic degradation. Result indicated that PN-GN had lower internal resistance, larger specific surface area, and higher electrochemical activity than single-doped graphene materials. The catalytic activity of GN was greatly improved by P/N codoping. When PN-GN (P8.4%-N7.6%-500°C) was used as catalyst (current of 20mA, initial pH of 7, reaction time of 60min), the degradation efficiency of APAP reached 98.2% ± 1.8%, which was 17.9% ± 3.6% higher than P-codoped graphene (P-GN), 14.7% ± 4.6% higher than N-codoped graphene (N-GN), and 54.0% ± 5.2% higher than GN. After 180min of reaction, the degradation efficiency of total organic carbon (TOC) was 78.5%. The reaction conditions were optimized and the degradation pathway of APAP was estimated to elucidate the catalytic mechanism. The main active substances generated in the system were identified as active chlorine and O2•-.

Assessment of the treatment efficiency of some polycyclic aromatic hydrocarbon (PAHs) in the water by doped TiO2

Treatment of persistent organic pollutants by advanced oxidation processes is a trend nowadays because of its efficiency. Through studies, it has been found that enhanced oxidation processes can treat organic pollutants that are difficult to decompose due to OH radicals and can convert those substances into nontoxic substances which areH2O và CO2. TiO2is a strong oxidizing agent; especially with the addition of catalysts, it is highly likely to be able to to treat persistent pollutants. PAHs are a class of polycyclic aromatic hydrocarbons that are highly toxic and persistent in the environment. The treatment of PAHs with 1% Fe-doped TiO2 coated on silica gel combined with using a 365nm UV lamp model initially produced certain results. Treatment efficiency is up to over 90% after 48 hours. On that basis, the article proposes a feasible solution for the treatment of PAHs in particular and toxic organic substances in general.

Vital Role of Synthesis Temperature in Co–Cu Layered Hydroxides and Their Fenton-like Activity for RhB Degradation

Cu and Co have shown superior catalytic performance to other transitional elements, and layered double hydroxides (LDHs) have presented advantages over other heterogeneous Fenton catalysts. However, there have been few studies about Co–Cu LDHs as catalysts for organic degradation via the Fenton reaction. Here, we prepared a series of Co–Cu LDH catalysts by a co-precipitation method under different synthesis temperatures and set Rhodamine B (RhB) as the target compound. The structure-performance relationship and the influence of reaction parameters were explored. A study of the Fenton-like reaction was conducted over Co–Cu layered hydroxide catalysts, and the variation of synthesis temperature greatly influenced their Fenton-like catalytic performance. The Co–Cut=65°C catalyst with the strongest LDH structure showed the highest RhB removal efficiency (99.3% within 30 min). The change of synthesis temperature induced bulk-phase transformation, structural distortion, and metal–oxygen (M–O) modification. An appropriate temperature improved LDH formation with defect sites and lengthened M–O bonds. Co–Cu LDH catalysts with a higher concentration of defect sites promoted surface hydroxide formation for H2O2 adsorption. These oxygen vacancies (Ovs) promoted electron transfer and H2O2 dissociation. Thus, the Co–Cu LDH catalyst is an attractive alternative organic pollutants treatment.

Oxidation of aqueous p-Nitroaniline by pulsed corona discharge

Toxic and potentially carcinogenic aromatic amines widely used in industry find their way to the aquatic environment. Gas-phase pulsed corona discharge (PCD) treatment of recalcitrant organic pollutants is a promising energy-efficient advanced oxidation process. The study assessed the energy efficiency of PCD in oxidation of p-nitroaniline (PNA), a persistent and ubiquitous pollutant of the aquatic environment. The effect of process control parameters on the energy efficiency of PNA degradation was studied including pH, gas–liquid contact surface and applied pulse repetition frequency. The results showed that PCD surpasses the commercially available competitor, Fenton reagent, for about three times. The reaction intermediates were analysed by HPLC-MS(ESI ± ) resulting in proposal of two transformation products. The PNA oxidation process followed the second-order kinetics showing the reaction rate coefficient moderately increasing with the contact surface and decreasing with the pulse repetition frequency. The acute toxicity of PNA solutions decreased substantially on the course of PCD treatment.

Performance, Reaction Pathway and Kinetics of the Enhanced Dechlorination Degradation of 2,4-Dichlorophenol by Fe/Ni Nanoparticles Supported on Attapulgite Disaggregated by a Ball Milling-Freezing Process.

Attapulgite (ATP) disaggregated by a ball milling–freezing process was used to support Fe/Ni bimetallic nanoparticles (nFe/Ni) to obtain a composite material of D-ATP-nFe/Ni for the dechlorination degradation of 2,4-dichlorophenol (2,4-DCP), thus improving the problem of agglomeration and oxidation passivation of nanoscale zero-valent iron (nFe) in the dechlorination degradation of chlorinated organic compounds. The results show that Fe/Ni nanoparticle clusters were dispersed into single spherical particles by the ball milling–freezing-disaggregated attapulgite, in which the average particle size decreased from 423.94 nm to 54.51 nm, and the specific surface area of D-ATP-nFe /Ni (97.10 m2/g) was 6.9 times greater than that of nFe/Ni (14.15 m2/g). Therefore, the degradation rate of 2,4-DCP increased from 81.9% during ATP-nFe/Ni application to 96.8% during D-ATP-nFe/Ni application within 120 min, and the yield of phenol increased from 57.2% to 86.1%. Meanwhile, the reaction rate Kobs of the degradation of 2,4-DCP by D-ATP-nFe/Ni was 0.0277 min−1, which was higher than that of ATP-nFe/Ni (0.0135 min−1). In the dechlorination process of 2,4-DCP by D-ATP-nFe/Ni, the reaction rate for the direct dechlorination of 2,4-DCP of phenol (k5 = 0.0156 min−1) was much higher than that of 4-chlorophenol (4-CP, k2 = 0.0052 min−1) and 2-chlorophenol (2-CP, k1 = 0.0070 min−1), which suggests that the main dechlorination degradation pathway for the removal of 2,4-DCP by D-ATP-nFe/Ni was directly reduced to phenol by the removal of two chlorine atoms. In the secondary pathway, the removal of one chlorine atom from 2,4-DCP to generate 2-CP or 4-CP as intermediate was the rate controlling step. The final dechlorination product (phenol) was obtained when the dechlorination rate accelerated with the progress of the reaction. This study contributes to the broad topic of organic pollutant treatment by the application of clay minerals.

Enhancement Photocatalytic Activity of Mn Doped Cds/Zno Nanocomposites for the Degradation of Methylene Blue Under Solar Light Irradiation

Abstract In this study, Mn doped CdS/ZnO nanocomposites synthesized by co-precipitation method and its photocatalytic activity was tested using methylene blue under solar light irradiation. The prepared hybrid nanocomposites are characterized by using different physicochemical techniques including XRD, FESEM, EDX, TEM, UV-vis DRS and PL analysis. From the XRD analysis, Mn doped ZnO/CdS nanocomposite diffraction peaks only reflect the binary crystalline structures of ZnO and CdS. However, there is no characteristic peak of Mn is found that may be because of low content of Mn doped on ZnO/CdS. But Mn (2.9 wt%) was detected in the Mn doped ZnO/CdS nanocomposite, which was measured by EDX analysis. The FESEM and TEM results exhibit the surface particle of Mn doped ZnO/CdS nanocomposite which have spherical nature and confirmed the formation of Mn doped ZnO/CdS nanocomposites. The photocatalytic degradation results have revealed that the Mn doped CdS/ZnO nanocomposites exhibit admirable activity toward the photocatalytic degradation of the MB. The reason for excellent photocatalytic activity of Mn doped CdS/ZnO nanocomposites indicates the absorbance band shifted to red region and reduction of recombination of photogenerated electron-hole, which is in good agreement with UV-visible DRS analysis and PL study results. The fitted kinetic plots showed a pseudo-first-order reaction model and the appropriate rate constants were found to be 0.0068 min−1, 0.00846 min−1, and 0.0188 min−1, for ZnO, 25 % CdS/ZnO, and 0.8 mol% Mn doped CdS/ZnO nanocomposites, respectively. The maximum photocatalytic activity was achieved by 0.8 mol% Mn doped CdS/ZnO nanocomposites with a 95% degradation efficiency of MB. Hydroxyl and superoxide radicals, having a vital role in the degradation of MB, confirmed scavenging experiments. In addition, the recycling tests displays that the Mn doped CdS/ZnO nanocomposites have shown good stability and long durability. The enhanced photodegradation activity of Mn doped CdS/ZnO nanocomposites indicates the potential of the nanocomposite for the treatment of organic pollutants from the textile wastewater.

Preparation of carbon quantum dots/TiO2 composite and application for enhanced photodegradation of rhodamine B

Titanium dioxide-coated carbon quantum dots (CQDs/TiO2)-based composite was prepared by sol-gel hydrolysis and studied as a catalyst for photodegradation of rhodamine B (RhB) in aqueous solution. The photocatalytic activity and stability of the composite was investigated under visible light. The structure, optical and electrochemical properties of as-prepared samples were characterized by means of SEM, TEM, XRD, XPS, FT-IR, BET, PL, UV–vis/DRS and EIS analyses. The results show that the absorption intensity of the CQDs/TiO2 composite is increased compared to that of TiO2. In addition, the absorption wavelength of the composite material is red-shifted to the visible region. When the content of CQDs in composite is 5 % (based on the mass of TiO2), the obtained CQDs/TiO2 exhibits excellent catalytic activity for the degradation of RhB. The degradation rate of CQDs/TiO2 is 85.47 %, which is 5.5 times higher than that of the pure TiO2. The catalytic degradation rate of RhB remained above 80 % even after 4 cycles. The photocatalytic mechanism of RhB by CQDs/TiO2 reveal holes (h+), superoxide anion radical (•O2–), hydrogen peroxide (H2O2), and hydroxyl radical (•OH) are the main active species in the photocatalytic process. The oxidizing abilities of the four substances are in the order of •O2– > h+ > •OH > H2O2. This work highlights the enhanced photocatalytic performance of CQDs/TiO2 composite for the treatment of organic pollutants.

Enhanced Electro-Fenton Degradation of Ciprofloxacin by Membrane Aeration

Electro-Fenton is a widely used electrochemical advanced oxidation process for the treatment of refractory organic pollutants, in which O2 input is required to generate hydrogen peroxide. The aeration mode directly affects the dissolution and stability of O2 bubbles in the solution, thus the rate of degradation. Herein, membrane aeration was introduced to the electro-Fenton degradation of ciprofloxacin in which O2 was dispersed into the liquid phase in the form of microbubbles through the ceramic membrane. Microbubbles can greatly improve the gas–liquid mass transfer efficiency of unit volume O2 to obtain an ultrahigh concentration of dissolved O2 up to 46 mg/L, thus improving the reaction rate. The effects of aeration mode, applied current, membrane aperture, aeration rate, and ciprofloxacin concentration on degradation rate were studied. Compared with the conventional electro-Fenton process using plastic pipe aeration, the membrane aeration-enhanced electro-Fenton (MAEF) system achieved a significant improvement in the degradation rate, and the reaction time required to achieve a 97% degradation ratio was remarkably reduced from 4 h to 10 min. Membrane aeration is an efficient approach to facilitating heterogeneous catalysis reactions involving the gas phase.