Bisphenol A In Aqueous Solution Research Articles

Adsorption performance of the functional COFs for removal of bisphenol A: Molecular dynamic simulations

The inherent structural features of the covalent organic frameworks (COFs) play a crucial role in determining their adsorption performances for bisphenol A (BPA). The computational methods were advantageous in unraveling intrinsic molecular properties about their performances. Herein, some COFs with different functional groups (–COOH, –NH2, –NO2 and –CF3) were designed to demonstrate the efficacy of the functional COFs for adsorbed BPA in gas phase and aqueous solution. The density functional theory (DFT) and Grand Canonical Monte Carlo (GCMC) methods were used to analyze the interaction energy between COFs and BPA, structure properties, and adsorption performances etc.. The results indicated that the addition of strong electronegative functional groups in COFs increased these COFs’ isosteric heat of adsorption (Qst) (TpBD-(COOH)2 > TpBD-(CF3)2 > TpBD-(NH2)2 > TpBD-(NO2)2 > TpBD) for gas phase BPA, but their introduction also reduced the pore size of COFs (TpBD > TpBD-(COOH)2 > TpBD-(NH2)2 > TpBD-(CF3)2 > TpBD-(NO2)2). However, these functional COFs demonstrated the stronger the adsorption capacity for gas phase BPA (At 298 K and 1 bar, the BPA uptake of TpBD-(COOH)2, TpBD-(NH2)2, TpBD, TpBD-(NO2)2 and TpBD-(CF3)2 was 242.52, 232.43, 219.31, 206.64 and 197.73 mg/g, respectively.). The amount of BPA adsorbed by functional COFs was the result of the synergistic effect of the electronegativity of functional groups and the pore size. Molecular dynamic (MD) simulation performed the same phenomenon for BPA in aqueous solution. In addition, the higher temperature will decrease the adsorption amount of BPA by COF, but increase its desorption ability.

MWCNTs Decorated with TiO2 as Highly Performing Filler in the Preparation of Nanocomposite Membranes for Scalable Photocatalytic Degradation of Bisphenol A in Water.

Bisphenol A (BPA), an endocrine-disrupting compound with estrogenic behavior, is of great concern within the scientific community due to its high production levels and increasing concentration in various surface aquifers. While several materials exhibit excellent capacity for the photocatalytic degradation of BPA, their powdered nature and poor chemical stability render them unsuitable for practical application in large-scale water decontamination. In this study, a new class of nanocomposite membranes based on sulfonated polyethersulfone (sPES) and multiwalled carbon nanotubes decorated with TiO2 nanoparticles (MWCNTs-TiO2) were investigated as efficient and scalable photocatalysts for the photodegradation of BPA in aqueous solutions. The MWCNTs-TiO2 hybrid material was prepared through a facile and inexpensive hydrothermal method and extensively characterized by XRD, Raman, FTIR, BET, and TGA. Meanwhile, nanocomposite membranes at different filler loadings were prepared by a simple casting procedure. Swelling tests and PFG NMR analyses provided insights into the impact of filler introduction on membrane hydrophilicity and water molecular dynamics, whereas the effectiveness of the various photocatalysts in BPA removal was monitored using HPLC. Among the different MWCNTs-TiO2 content nanocomposites, the one at 10 wt% loading (sP-MT10) showed the best photoactivity. Under UV irradiation at 254 nm and 365 nm for 240 min, photocatalytic oxidation of 5 mg/L bisphenol A by sP-MT10 resulted in 91% and 82% degradation, respectively. Both the effect of BPA concentration and the membrane regenerability were evaluated, revealing that the sP-MT10 maintained its maximum BPA removal capability over more than 10 cycles. Our findings indicate that sP-MT nanocomposite membranes are versatile, scalable, efficient, and highly reusable photocatalysts for the degradation of BPA, as well as potentially for other endocrine disruptors.

Cellulose-incorporated imprinted materials with amphiphilic crosslinking structure for selective adsorption of bisphenol A

The development of cost-effective and easy-operate adsorbents with tunable adsorption performance is of great importance while remains a big challenge. Herein, cellulose-incorporated imprinted material (CMC-MIPs) with solvent-regulated adsorption property was designed and synthesized using the functionalized cellulose (CMC-MA) as main cross-linker with the assistance of co-crosslinking agent divinyl benzene for selective adsorption of bisphenol A (BPA). Styrene was used as functional monomer to interact with BPA through π-π stacking interaction. And CMC-MA could interact with BPA by multi-hydrogen bonding to strengthen the binding interaction. Adsorption experiments demonstrated that the obtained CMC-MIPs exhibited high adsorption capacity (16.23 mg/g) and excellent selectivity (imprinting factor: 16.07) towards BPA. And CMC-MIPs can easily adsorb BPA in aqueous solution, while release most of the adsorbed BPA in organic media (i.e., methanol or ethanol), indicating excellent solvent-regulated adsorption/release property. The developed CMC-MIPs were successfully employed for selective adsorption of BPA from milk samples with satisfactory recoveries. The proposed construction strategy will offer new sights on the fabricating the cellulose-introduced imprinted materials with selective adsorption capability for target analytes.

Green Synthesis of ZnO/BC Nanohybrid for Fast and Sensitive Detection of Bisphenol A in Water

A nanohybrid of zinc oxide and biochar (ZnO/BC) with high conductivity was green synthesized using a simple hydrothermal method, and utilized for the sensitive detection of bisphenol A (BPA) by coating the nanohybrid film on an electrode of glassy carbon. The ZnO/BC presented greatly improved electrocatalytic performance and electron transfer ability compared to the zinc oxide and biochar. The ZnO/BC film-coated electrode could detect the BPA in aqueous solution within 3 min while neglected interference from higher concentrations of regularly existing ions and similar concentrations of estradiol (E2), phenol, dichlorophenol (DCP), and ethinylestradiol (EE2). Under optimal conditions, the linear range of BPA detection was 5 × 10−7~1 × 10−4 mol/L, with a detection limit of 1 × 10−7 mol/L, and the detection sensitivity was 92 mA/M. In addition, the ZnO/BC electrode could detect BPA in a real water sample with good signal recovery. This electrode, with the advantages of an easy preparation, low cost, and fast response time, could be potentially applicable for environmental monitoring.

Microwave solvothermal-assisted calcined synthesis of Bi2WxMo1−XO6 solid solution photocatalysts for degradation and detoxification of bisphenol A under simulated sunlight irradiation

• Bi 2 W 0.25 Mo 0.75 O 6 microspheres showed the best photocatalytic activity. • Removal efficiencies of BPA and TOC were 96.2% and 87.1% at 15 mg L −1 BPA. • Photo-hole, O 2 − and OH contributed to photocatalytic degradation of BPA. • Degradation pathways were proposed according to intermediates and active species. • Bioluminescence/QSAR analysis confirmed toxicity reduction during BPA degradation. A series of (x = 0, 0.25, 0.5, 0.75, 1) solid solution photocatalysts was designed and synthesized by the combination of microwave solvothermal method and post-treatment calcination. The physicochemical and optical properties of the as-prepared solid solution photocatalysts were characterized by various techniques. The photocatalytic activity was also evaluated through the photodegradation of bisphenol A (BPA) under simulated sunlight irradiation. Results showed that all photocatalysts were flower-like, and the Bi 2 W 0.25 Mo 0.75 O 6 microspheres showed the best photocatalytic activity. The removal efficiencies of BPA and total organic carbon were 96.2% and 87.1% at BPA concentration of 15 mg L −1 in 120 and 180 min, respectively. During the reaction process, O 2 − and h + played the dominant role, while OH also contributed to the BPA degradation. Twelve intermediate products were identified, and they were gradually mineralized to CO 2 and H 2 O. On the basis of the analysis of active species and intermediates determined, the main degradation pathways for BPA were proposed, namely, hydroxylation, alkylic-oxidation, dehydrogenation, and aromatic ring opening. The toxicity change during BPA degradation was also investigated by standardized bioluminescence assay of inhibition rate on luminescent bacterium Vibrio qinghaiensis sp . Q67 in combination with quantitative structure–activity relationship analysis. The inhibition effect of BPA and its intermediates to V. qinghaiensis sp . Q67 was gradually eliminated with the decomposition of BPA. In conclusion, the Bi 2 W 0.25 Mo 0.75 O 6 is an effective photocatalyst for degradation and toxicity reduction of BPA in aqueous solution.

Exploring the Ability of Luminescent Metal Assemblies to Bind and Sense Anionic or Ionizable Analytes A Ru(phen)2bipy-Based Dizinc Complex for Bisphenol A (BPA) Recognition.

The synthesis of a new RuII complex, in which the metal is coordinated by two 1,10-phenanthroline ligands and a 2,2′-bipyridyl unit linked, via methylene bridges in its 4 and 4′ positions, to two 1,4,7,10-tetraazacyclododecane (cyclen) macrocycles ([Ru(phen)2L]2+) is reported. Protonation and ZnII binding by [Ru(phen)2L]2+ have been analyzed by potentiometric titration, evidencing the formation of mixed hetero-binuclear and hetero-trinuclear ZnII/RuII complexes. These complexes were tested as bis-phenol A (BPA) binders. Only the dizinc complex with [Ru(phen)2L]2+ is able to bind BPA in aqueous solution, affording a remarkably stable {Zn2[Ru(phen)2L]BPA(H−2)}4+ adduct at neutral pH, in which BPA is bound in its doubly deprotonated form to the two ZnII ions. BPA binding was found to quench the luminescence emission of the RuII(phen)2bipy core. Although the quenching effect is modest, this study demonstrates that appropriately designed dizinc complexes can be used for binding and optical sensing of BPA in water.

Study of Fe3O4/PS System in Degrading BPA in Aqueous Solution

The degradation of bisphenol A (BPA) by Fe3O4/persulfate system was investigated in aqueous solution. The influences of the initial concentrations of Fe3O4, persulfate (PS) and BPA, pH value, and initial reaction temperature on BPA removal were studied. The radical species was investigated by adding excessive dose of scavenger (methanol (MeOH) and tert-butanol (TBA)) into Fe3O4/PS system for the purpose of radical scavenging. The degradation products of BPA were detected by gas chromatography-mass spectrometry (GC-MS). The recyclability of Fe3O4 was also evaluated. The BPA removal rate of 80.7% was achieved under the following conditions: [BPA]0 = 1 mg L-1, [PS]0 = 0.2 mM, [Fe3O4]0 = 0.1 g L-1, T0 = 20 ± 1 ºC, pH0 = 6.8 ± 0.2. The results confirmed that the main free radicals in the reaction process were sulfate radicals, followed by hydroxyl radicals. Some intermediate products of BPA degradation, such as phenols, benzoquinones and benzoic acid were identified by GC-MS.

Sonophotocatalytic (1.7 MHz, 254 nm) destruction of Bisphenol-A in aqueous solutions

Bisphenol A (BPA) an organic compound largely used in the plastic industry as a monomer. The micropollutant BPA (43.8 μM) was employed under conditions of high-frequency ultrasound (1.7 MHz, 25 W) and ultraviolet radiation (254 nm). To enhance degradation a Fenton-like oxidation system was used, including persulfate as an oxidizing agent and ferrous iron (Fe (II))) as a catalyst. Experiments were carried out in a flow sonophotoreactor, flow rate 0.5 l/min. The progress of the treatment of Bisphenol-A solution has been monitored in terms of reduction in the concentration (HPLC) and dissolved organic carbon (DOC). A large synergistic effect (2.4) was shown in the oxidation of Bisphenol-A from the combined effect of two directed at each other sources of ultrasound. The efficacy of combined approaches was generally higher than individual treatment methods of sonolysis (87%) and photolysis (15%) in 240 min of treatment. Complete oxidation of BPA is achieved in the {UV/US/Fe2+/S2O8 2-} system in 120 minutes, however, mineralization reaches (50%), possibly due to the lack of an oxidizing agent. The reaction rates of Bisphenol A degradation and mineralization increase in the order: {UV} <{US} <{Fe2+/S2O8 2-} <{US/Fe2+/S2O8 2-} <{UV/US/Fe2+/S2O82-}.

A Novel Catalytic Process for Degradation of Bisphenol A in Aqueous Solutions Using Fe Supported on Alginate/Carboxymethylcellulose

This work aimed to synthesize new heterogeneous iron-based catalysts supported on biopolymers (alginate (Alg), carboxymethylcellulose (CMC), xanthan gum (GX) and chitosan (Qui)) and their mixtures—and their mixtures—to evaluate their degradation Bisphenol A (BPA) in aqueous solutions. The Alg-Fe, QuiGa-Fe and CMC-Fe, CMCGX-Fe, AlgCMC-Fe, AlgGX-Fe catalysts were prepared and characterized by SEM, FTIR and FAAS. For the degradation of BPA was evaluated and AlgCMC-Fe was considered the best catalyst for having high catalytic activity and less leaching of iron ions in the reaction medium. Then, the kinetics of BPA degradation by Fenton oxidation process were investigated varying: H2O2 concentration, AlgCMC-Fe content, pH, reaction time and initial BPA concentrations. The degradation of BPA was monitored by HPLC–DAD and the results showed that AlgCMC-Fe were able to promote total degradation of BPA in aqueous solutions a (2.00 mg L−1 BPA) at a pH close to neutral, with a recycling capacity of up to three times with the same efficiency. The pseudo-second-order was the most appropriate model to describe the kinetic mechanism.

A magnetic hydrophilic molecularly imprinted material with multiple stimuli-response properties for efficient recognition of bisphenol A in beverages.

A magnetic hydrophilic molecularly imprinted material (MIM) with multiple stimuli-responses was prepared for efficient recognition of bisphenol A (BPA). MIM consisted of a magnetic core, an inner silica dioxide shell and an outer hydrophilic polymer shell, responsive for rapid magnetic separation, protection of the magnetic core and pH-/thermo-sensitivity to BPA, respectively. Controlled adsorption and release of BPA by pH/temperature regulation were realized through the reversible components of poly[N-isopropylacrylamide-co-2-(dimethylamino)ethyl methacrylate (NIPAM-DMAEMA)] (PND). The resultant MIM possessed superior affinity, selectivity and kinetics to BPA in aqueous solution. MIM was successfully applied to detect BPA in beverages via dispersive solid-phase extraction (d-SPE) coupled with high performance liquid chromatography (HPLC), exhibiting satisfactory recoveries of 80.70-108.18% with relative standard deviations (RSD) below 6.08%. The limit of detection of BPA was obtained as low as 3.75nmol/L. The versatile MIM could be a promising alternative for extraction/removal of BPA in complicated samples by multiple-stimuli regulations.

Photocatalytic degradation of bisphenol-A in aqueous solution by calcined PbO semiconductor irradiated with visible light

Photocatalytic degradation of bisphenol-A in aqueous solution by calcined PbO semiconductor irradiated with visible light

Activation of persulfate with biochar for degradation of bisphenol A in soil

In this study, a new alternative activator, biochar (BC) pyrolyzed by waste biomass—lychee branch, was applied in persulfate (PS) -based remediation for bisphenol A (BPA) in soils. Radical species, solution pH, dose of PS and BC were studied to evaluate the performance of PS activation by BC to degrade BPA in aqueous solution. The results show that BC can efficiently activate PS to generate sulfate radicals and hydroxyl radicals to degrade BPA high efficiently. The increase of PS and BC dosage can increase BPA removal rate, and a lower pH is benefit for the BPA degradation in aqueous solution. In addition, the degradation intermediates of BPA were characterized and the degradation pathways were proposed. Furthermore, the PS/BC system is most efficient for BPA degradation compared with other oxidants. For soil spiked with 31.93 mg kg−1 BPA, BC can also activate PS and degrade BPA effectively. The increase of BC and PS dose cannot always increase BPA degradation because of the competition of readily oxidizable matter introduced by BC itself and/or quenching of sulfate radicals. During BPA degradation in soil, the pH value drops less than those in literatures on PS oxidation of organic contaminants in soil by other activation methods, which can alleviate soil acidification in the remediation process. The results of this study suggest a novel technique for potential application in in-situ remediation of organic contaminated sites.

Synthesis of sulfonated polystyrene sphere based magnesium silicate and its selective removal for bisphenol A

In this work, a sulfonated polystyrene sphere (SPS) based magnesium silicate nanocomposite (SPS@MgSix) with superior adsorption capability has been prepared for the removal of BPA, a kind of emerging pollution existed in various wastewaters. It was obtained by in situ growth of the Talc-phase Mg3Si4O9(OH)10 (MgSi) on the surface of SPS, in which the SPS substrate can effectively avoid the agglomeration of MgSi. Scanning electron microscope (SEM) has shown that interwoven nano-sized MgSi uniformly distributes on the surface of SPS, leading to a high adsorption capacity (Q0: 357.14 mg L−1) for removing bisphenol A (BPA). It is worth noting that these composite materials also exhibit relative good adsorption capability even under high-concentration salt conditions, for example, the adsorption capacity still keeps at about 331.14 mg g−1 in the presence of high concentration Na+ or Ca2+. The Zeta potential tests indicate that the high adsorption capacity may be related to an electrostatic interaction between SPS@MgSix and BPA. The excellent adsorption behaviors of SPS@MgSix show that it is a highly promising candidate for removing BPA in aqueous solution.

Fabrication of highly porous N/S doped carbon embedded with ZnS as highly efficient photocatalyst for degradation of bisphenol

In the present study, a novel nanocomposite has been successfully fabricated that contain nitrogen and sulphur doped porous carbon and ZnS nanoparticles. The fabricated nanocomposite has been used as a photocatalyst for the photocatalytic degradation of bisphenol-A (BPA) under visible light. The prepared nanocomposite was characterized using FT-IR, XRD, Raman, SEM, TEM, SAED, BET and XPS. The results revealed that the fabricated nanocomposite (ZnS/NSDC) exhibited highly porosity due to large surface area 642.24 cm2/g and promising pore volumes. ZnS/NSDC nanocomposite was showed excellent photocatalytic performance for BPA degradation. During the photocatalytic degradation of BPA, several intermediate products with the molecular mass including m/z 151, m/z 133, and m/z 137 were observed using LC-MS analyses. The experimental outcomes are supported by theoretical calculations via, density functional theory (DFT) and elucidate the photocatalytic degradation mechanism of BPA. These efforts suggest that the fabricated ZnS/NSDC nanocomposite exhibits excellent properties to severe threat to environment and can be used as a reusable photocatalyst for the degradation of BPA in aqueous solution.

Removal of bisphenol A by laccases from Pleurotus ostreatus and Pleurotus pulmonarius and evaluation of ecotoxicity of degradation products

Bisphenol A (BPA) is an endocrine disruptor compound, that is continuously released into the environment and is barely degraded in wastewater treatment plants. In this work, crude laccases from Pleurotus ostreatus and Pleurotus pulmonarius were used for the first time to degrade BPA in aqueous solution. The residual BPA was quantified by HPLC and the BPA metabolites produced by action of the laccases were identified by GC–MS. BPA at 100mg/L and 200mg/L (0.88mmol/L) were 100% and 85% removed, respectively, in a 1h reaction by both fungal laccases at a concentration of 8U/L. Thirteen aromatic and aliphatic BPA metabolites were identified, including p-isopropenylphenol, methylpent-3-oic acid, ethyl-3-ethoxy propanoate, and 4-ethyl-2-methoxyphenol. The acute BPA toxicity decreased from 85% to less than 5% using the P. ostreatus laccase. On the other hand, P. pulmonarius laccase, did not caused reduction in toxicity, possibly because at least one BPA metabolite was as toxic as the parent compound itself. The results of this study suggest a feasible method for the complete removal of BPA from polluted environments using crude laccase from P. ostreatus.

Degradation of bisphenol-A by dielectric barrier discharge system: influence of polyethylene glycol stabilized nano zero valent iron particles

In this study we report the synthesis and catalytic properties of polyethylene glycol stabilized nano zero valent iron particles (PEG-nZVI) added to the dielectric barrier discharge (DBD) system to induce photo-Fenton process in the degradation of bisphenol A (BPA) in aqueous solution. The influence of operating parameters such as solution pH, initial concentration of the modelled pollutant and PEG-nZVI dosage on the extent of BPA degradation was investigated. The residual concentration of BPA and its intermediates were determined using high performance liquid chromatography (HPLC) and liquid chromatography mass spectrometry (LCMS). The high resolution scanning electron microscope (HRSEM), x-ray diffraction (XRD), Brunauer–Emmett-Teller (BET) surface area, and x-ray photoelectron spectroscopy (XPS) analysis confirmed the formation of filamentous, high surface area iron nanoparticles in the zero valent state. The BPA mineralization rate was monitored using total organic carbon (TOC) analyser. 100% BPA removal was achieved with DBD/PEG-nZVI system within 30 min compared to 67.9% (BPA) with DBD alone after 80 min. The complete BPA removal within a short reaction time was attributed to the existence of a synergetic effect in the combined DBD/PEG-nZVI system. Five new transformation products of BPA namely: 4-nitrophenol (C6H5NO3), 4-nitrosophenolate (C6H4NO2), 4-(prop-1-en-2-yl) cyclohexa-3,5-diene-1,2-dione, (C9H8O2), 4-(2-hydroxylpropan-2-yl)cyclohexane-3,5-diene-1,2-dione (C9H10O3), and 1,2-dimethyl-4-(2-nitropropan-2-yl)benzene (C9H10NO4) were identified. BPA degradation proceeded via ozonation, hydroxylation, dimerization, and decarboxylation and nitration step. The combined DBD/photo-Fenton-induced process was found to be the most efficient in the elimination of BPA in aqueous solutions and DBD alone.

An electrochemical sensor based on molecularly imprinted polypyrrole/graphene quantum dots composite for detection of bisphenol A in water samples

Bisphenol A (BPA) is an important endocrine disrupter in environments, for which sensitive and selective detection methods are highly necessary to carry out its recognition and quantification. Here a novel electrochemical sensor was developed based on molecularly imprinted polypyrrole/graphene quantum dots (MIPPy/GQDs) composite for the detection of bisphenol A (BPA) in water samples. A MIPPy/GQDs composite layer was prepared by the electropolymerization of pyrrole on a glassy carbon electrode with BPA as a template. The MIPPy/GQDs composite could specifically recognize BPA in aqueous solutions, which resulted in the decrease of peak currents of K3[Fe(CN)6] at the MIPPy/GQDs) modified electrode in cyclic voltammetry (CV) and differential pulse voltammetry (DPV). There was a linear relationship between BPA concentrations ranging from 0.1μM to 50μM and the response value (ΔIDPV) in DPV, with a limit of detection of 0.04μM (S/N=3). The sensor was applied for the detection of BPA in tap and sea water samples, with recoveries of 94.5% and 93.7%, respectively. The proposed method provides a powerful tool for rapid and sensitive detection of BPA in environmental samples.

Water-compatible temperature and magnetic dual-responsive molecularly imprinted polymers for recognition and extraction of bisphenol A

Versatile molecularly imprinted polymers (MIPs) have been widely applied to various sample matrices, however, molecular recognition in aqueous media is still difficult. Stimuli-responsive MIPs have received increasing attentions due to their unique feature that the molecular recognition is regulated by specific external stimuli. Herein, water-compatible temperature and magnetic dual-responsive MIPs (WC-TMMIPs) with hydrophilic brushes were prepared via reversible addition-fragmentation chain transfer precipitation polymerization for reversible and selective recognition and extraction of bisphenol A (BPA). Transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR) and vibrating sample magnetometry (VSM) as characterization methods were used to examine the successful synthesis of polymers, and the resultant WC-TMMIPs showed excellent thermosensitivity and simple rapid magnetic separation. Controlled adsorption and release of BPA by temperature regulation were investigated systematically, and the maximum adsorption and removal efficiency toward BPA in aqueous solutions were attained at 35°C and 45°C, respectively, as well as a good recoverability was exhibited with the precision less than 5% through five adsorption–desorption cycles. Phenolic structural analogs were tested and good recognition specificity for BPA was displayed. Accordingly, the WC-TMMIPs were employed as adsorbents for magnetic solid-phase extraction (MSPE) and packed SPE of BPA from seawater samples. Using the two modes followed by HPLC-UV determination, excellent linearity was attained in the range of 0.1–14.5μM and 1.3–125nM, with low detection limits of 0.02μM and 0.18nM, respectively. Satisfactory recoveries for spiked seawater samples were achieved ranging from 86.3–103.5% and 96.2–104.3% with RSD within 2.12–4.33%. The intelligent WC-TMMIPs combining water-compatibility, molecular recognition, magnetic separation, and temperature regulation proved potentially applicable for selective identification, controlled adsorption/release and high-efficiency enrichment/removal of trace targets in complicated aqueous media.

Voltammetric Sensing of Endocrine Disruptor (Bisphenol A) Based on a Reduced Graphene Oxide/Carbon Nanotube/Gold Nanoparticles Nanocomposite Modified Screen-Printed Electrode

Bisphenol A (BPA) (2,2-bis(4-hydroxyphenyl propane, C15H16O2) is a key monomer ubiquitously used in the production of polymers, polycarbonate plastics, sealants, epoxy resins, the lining of food cans etc1. However, BPA could potentially interfere with the endocrine system of humans and is believed to be indicated in diverse pleiotropic actions in the brain and cardiovascular systems, various kinds of cancer, reproductive disorders, obesity, and birth defects, etc1. Given the deleterious effects of BPA and its omnipresent presence in our daily life, the development of a rapid, simple and sensitive analytical method for BPA measurement is critical. Several approaches are used to determine BPA2, which include but not limit to liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), enzyme-linked immunosorbent assay (ELISA), and liquid chromatography-electrochemical detector (LC-ECD). Although these methods could detect BPA sensitively, complex, time-consuming sample preparation protocols and expensive equipment used are major disadvantages. Electrochemical methods, on the other hand, are rapid, inexpensive, simple, and highly sensitive; moreover, they are amenable for fabrication of portable units. Herein, we present a facile and green approach to fabricate a highly sensitive electrochemical sensor for the determination of BPA in aqueous solution by using reduced graphene oxide (RGO), carbon nanotubes (CNT), and gold nanopaticles (AuNPs) modified screen-printed electrode (SPE). Graphene oxide (GO)/CNT nanocomposite was first deposited onto SPE, then electrochemically reduced to RGO/CNT at room temperature. Subsequently, AuNPs were electrochemically deposited in situ on RGO/CNT modified SPE. The morphology of bare SPE, GO/CNT-modified SPE, and RGO/CNT/AuNPs-modified SPE was characterized by scanning electron microscopy (SEM). Figures 2a, b, and c displays the SEM images of the working electrode part of bare SPE, GO/CNT-modified SPE, and RGO/CNT/AuNPs-modified SPE, respectively. The bare SPE, shows sheet-like structures with many small particles dispersed throughout (Figure 2a). These structures can be assigned as graphitic carbon powder, according to the composition of the electrode. Figure 2b demonstrates the CNT could improve the surface roughness and potentially bridge the graphene sheet and small particles of graphitic powder. After electrodeposition of AuNPs, the AuNPs are seen evenly distributed in the RGO/CNT network (Figure 2c). Based on particle size analysis of at least 100 particles in SEM images, the average size of AuNPs was 84.6 ± 23.6 nm. Figure 3a displays the cyclic voltammograms of ferri/ferrocyanide solution at bare, GO/CNT-, RGO/CNT-, and RGO/CNT/AuNPs-modified SPEs. The electrochemical response at the bare SPE (at 50 mV·s-1scan rate) displays a relatively slow electron transfer and an irreversible electrochemical process. When modified with GO/CNT, the peak separation increased along with a reduction in the redox peak current. After GO is reduced to RGO (i.e., became RGO/CNT modified SPE), as expected, the redox peak current raised with a much smaller peak separation, which implies that most of the oxygenated groups on GO were removed and electron transfer was improved. The electrochemical response was further significantly enhanced after the electrodeposition of AuNPs, which is attributable to the extraordinary catalytic ability, large surface-to-volume ratio, and excellent electrical conductivity of the AuNPs. Several important parameters, such as accumulation potential and time of differential pulse voltammetry, and pH value of buffer solution were investigated and optimized. Under the optimized conditions, the oxidation peak current in differential pulse voltammograms was proportional to BPA concentration in the range of 1.45 to 20 and 20 to 1,490 nmol/L of BPA, with an ultralow detection limit of 800 pmol/L (at signal/noise=3). Figure 1. Fabrication of RGO/CNT/AuNPs modified SPE Figure 2. SEM images of (a) bare, (b) GO/CNT-modified, and (c) RGO/CNT/AuNPs-modified SPEs Figure 3. (a) Cyclic voltammograms at bare and GO/CNT-, RGO/CNT-, and RGO/CNT/AuNPs-modified SPEs. (b) Peak currents for BPA detection in two linear ranges of 1.45 to 20 nM and 20 to 1,490 nM. Inset is an expanded view of measurements of 1.45 to 20 nM BPA.

Synergistic effect of Cu adsorption on the enhanced photocatalytic degradation of bisphenol A by TiO2/titanate nanotubes composites

The synergistic effect of Cu(II) adsorption on the enhanced photodegradation of bisphenol A (BPA) by TiO2/titanate nanotube (TNTs) was investigated under UV light irradiation. TNTs were fabricated by hydrothermal method and calcined at 500 °C for 4 h (TNT-500) to adsorb Cu(II) as well as to increase the photocatalytic activity. The TNT-500 exhibited an excellent adsorption ability on copper ions and the adsorption isotherm of Cu(II) followed the Langmuir model with the maximum adsorption capacity of 54 mg/g at pH 5. In addition, the photocatalytic activity of TNT-500 toward BPA degradation was significantly enhanced by factors of 20–34 after the adsorption of 5–40 mg/g Cu(II). The pseudo-first-order rate constant (kobs) for BPA photodegradation was highly dependent on Cu(II) concentration and an optimized value of 20 mg/L was obtained. The reaction rate of BPA by optimized Cu-loaded TNT-500 was 5.2 times higher than that of P25 TiO2. In addition, the photocatalytic activity of Cu-loaded TNT-500 was significantly enhanced at pH > 4.8 and can be recycled for at least 5 times to completely photodegrade BPA under 365 nm UV light irradiation. Results obtained in this study clearly indicate that TNTs are promising nanomaterials for coupled removal of Cu(II) and BPA in aqueous solutions which can open an avenue to develop an effective strategy for removal of mixed contaminants in water and wastewater treatment.