In situ electrochemical synthesis of graphene-poly(arginine) composite for p-nitrophenol monitoring

Efficient detection of p-nitrophenol via a polypyrrole flower-decorated nickel foam-based electrochemical sensor

p-Nitrophenol (p-NP) is known as a common contaminant found in wastewater, agricultural runoff, and industrial effluents which can degrade water quality and cause potential carcinogenic and toxic effects on the human body. Its detection is essential for public health, industrial safety, environmental protection, and regulatory compliance, underscoring its broad applicability. In this study, a novel electrochemical sensor based on polypyrrole (PPy) flowers assembled via nanotubes was developed for the sensitive determination of p-NP. The nickel (Ni) foam modified with PPy flowers functioned as the working electrode and showed selectivity toward p-NP in a phosphate buffer medium at pH 7.0. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were utilized for the sensitive determination of p-NP. Under the optimum conditions, the peak currents of DPV versus the concentrations of p-NP in the range of 0.01-20 nM showed a good linear relationship (R2 = 0.9943), and the limit of detection (LOD) was calculated to be 7.18 pM (signal-to-noise ratio of 3, S/N = 3). The fabricated electrochemical p-NP sensor exhibited high sensitivity, a low detection limit, and a low response time. The recoveries of p-NP in real samples of groundwater and tap water using the PPy Fls/Ni foam electrode were in the range of 91.0-108.4% with a relative standard deviation (RSD) in the range of 6.65%. Consequently, the PPy Fls/Ni foam electrode could be applied as a rapid, precise, and sensitive electrochemical sensor platform for aqueous p-NP quantification and determination.

High-performance fentanyl molecularly imprinted electrochemical sensing platform designed through molecular simulations

BACKGROUND

Fentanyl and its derivatives are a type of potent opioid analgesics, with the characteristics of diverse structure, high toxicity, extremely low content, and high fatality rate. Currently, they have become one of the most serious problems in international drug abuse control due to their extensive use in drug production and use. Therefore, the development of a rapid, sensitive, and accurate method for detecting trace fentanyl is of great significance. In this study, in view of its complex structure and trace concentration, a new molecular imprinting electrochemical sensor was developed through molecular simulations followed by experimental validation to detect trace fentanyl.

RESULTS

The process consisted of first obtaining the optimal functional monomer and its molar ratio through molecular simulations. The recognition sites of fentanyl-imprinted polymers were predicted to guide the synthesis of imprinted membranes with precision approach to ensure an efficient and accurate reaction process. Reduced graphene oxide (ErGO) was then deposited on glassy carbon electrode surface by electrochemical reduction to yield large numbers of active sites suitable for catalyzing reactions of fentanyl piperidine for promoted efficient electron transfer and amplified sensitivity of the sensor. Accordingly, fentanyl molecularly imprinted film was formed through one-step electropolymerization to yield greatly improved sensing selectivity due to the specific recognition of molecularly imprinted polymer. Under optimal experimental conditions, the fentanyl sensor showed an extended detection range of 3.84 × 10-9 mol L-1-1.72 × 10-6 mol L-1 and a detection limit of 1.28 × 10-9 mol L-1.

SIGNIFICANCE

A distinctive feature of this sensor is its molecularly imprinted polymerized membrane, which offers excellent specific recognition, thereby boosting the sensor's selectivity. Throughout the sensor's development process, molecular simulations were employed to steer the synthesis of molecularly imprinted polymers and predict the recognition sites of fentanyl-imprinted polymers. The experimental outcomes proved to align with the simulation data. The final sensor exhibited outstanding selectivity, repeatability, stability, and high sensitivity. The sensor was effectively used to reliably track fentanyl in human serum samples, with acceptable analytical reliability, suggesting its potential for practical applications.

Reaction mechanisms of chlorinated disinfection byproducts formed from nitrophenol compounds with different structures during chlor(am)ination and UV/post-chlor(am)ination

Nitrophenol compounds (NCs) have high formation potentials of disinfection byproducts (DBPs) in water disinfection processes, however, the reaction mechanisms of DBPs formed from different NCs are not elucidated clearly. Herein, nitrobenzene, phenol, and six representative NCs were used to explore the formation mechanisms of chlorinated DBPs (Cl-DBPs) during chlor(am)ination and UV/post-chlor(am)ination. Consequently, the coexistence of nitro and hydroxy groups in NCs facilitated the electrophilic substitution to produce intermediates of Cl-DBPs, and the different positions of nitro and hydroxy groups also induced different yields and formation mechanisms of Cl-DBPs during the chlorination and UV/post-chlorination processes. Besides, the amino, chlorine, and methyl groups significantly influenced the formation mechanisms of Cl-DBPs during the chlorination and UV/post-chlorination processes. Furthermore, the total Cl-DBPs yields from the six NCs followed a decreasing order of 2-chloro-3-nitrophenol, 3-nitrophenol, 2-methyl-3-nitrophenol, 2-amino-4-nitrophenol, 2-nitrophenol, and 4-nitrophenol during chlorination and UV/post-chlorination. However, the total Cl-DBPs yields from the six NCs during chloramination and UV/post-chloramination followed a quite different order, which might be caused by additional reaction mechanisms, e.g., nucleophilic substitution or addition might occur to NCs in the presence of monochloramine (NH2Cl). This work can offer deep insights into the reaction mechanisms of Cl-DBPs from NCs during the chlor(am)ination and UV/post-chlor(am)ination processes.

Electricity-driven dealkalization of bauxite residue based on thermodynamics, kinetics, and mineral transformation

High alkalinity content of bauxite residue is a major factor that hinders resource reutilization and pollutes the environment. Although acid neutralization is a direct and effective method, the amount of acid and secondary waste of sodium salt are still difficult problems to solve. Herein, we innovatively integrated an electric field into the acid neutralization dealkalization of bauxite residue and analyzed the dealkalization behavior by thermodynamics, kinetics, and mineral transformation. The results show that the pH of the anode chamber was maintained at the acidic levels of 3-6 after 30 min of galvanostatic electrolysis, and bauxite residue can realize dealkalization by acid neutralization. In the anode chamber, Na+ was released into the leachate via the reactions of Na3Al3Si3O12 and the removal of encapsulated soluble alkali. The stainless steel wire mesh anode exhibited its superiority and decreased the Na2O content in bauxite residue from 9.48 to 3.13% through convective mass transfer driven by the electric field and steady-state diffusion under stirring. This research provides a promising method for the electricity-driven dealkalization of bauxite residue, thus facilitating the development of multifield coupling theory and the application of electric fields in the alumina industry.

Strategy for establishing sensitive fluorescent sensor toward p-nitrophenol integrating magnetic molecularly imprinted materials and carbon dots

In this work, a sensitive fluorescent sensor toward p-nitrophenol (4-NP) integrating magnetic molecularly imprinted materials and carbon dots (CDs) was proposed. Magnetic material and CDs derived from K3 [Fe(CN)6] and glucose were simultaneously obtained through simple one-step hydrothermal process. Introducing of molecularly imprinted materials based magnetic solid phase extraction (MSPE) endowed the constructed fluorescent sensor with higher sensitivity and selectivity. The significant factors affecting the sensitivity of the sensor toward 4-NP were optimized. Good linearity was obtained between fluorescent intensity of CDs and different concentration of 4-NP from 0.08 to 62.5 μg L-1. The sensitivity of constructed sensor was very low with detection limit of 0.02 μg L-1. Reliable applicability was also proved by the well-pleasing recoveries of 94.2-97.8% with different spiked concentrations of 4-NP in real environmental waters.

Casting liquid PDMS on self-assembled bilayer polystyrene nanospheres to prepare a SERS substrate with two layers of nanopits for detection of p-nitrophenol

p-Nitrophenol (PNP) is widely used in pesticides, pharmaceuticals, and dyestuffs. It is vital to detect trace PNP in the environment, because it poses significant environmental hazards due to its high toxicity. In this paper, a new method was reported for preparing a SERS substrate with excellent SERS activity by combining self-assembly techniques and flexible materials. First, the three-dimensional (3D) polystyrene (PS) photonic crystal (PC) structural master was fabricated by stacking two layers of self-assembled PS nanospheres with different diameters. Polydimethylsiloxane (PDMS) with a complementary structure to the master was obtained by casting, curing and peeling off. Finally, the PDMS-Ag substrate was fabricated by sputtering a thin Ag layer on the PDMS structure. The enhancement factor (EF) of the PDMS-Ag substrate was calculated to be 2.90 × 109 by using 4-amino thiophenol (ATP) as the probe molecule, and the limit of detection (LOD) for ATP can reach 10-11 M. And the RSD of the SERS intensity for the peak at 1078 cm-1 on the PDMS-Ag substrates from batch to batch was within 2%, indicating the high reproducibility of the as-prepared substrate. The quantitative analysis of PNP was achieved with a LOD of 10-8 M. Therefore, the PDMS-Ag substrate exhibits high sensitivity and reproducibility, and it can detect PNP in trace amounts, with great potential for detecting other contaminants.

Decoration of alkalization-intercalated Ti3C2 with ZIF-8@ZIF-67-derived N-doped carbon nanocage for detecting 4-nitrophenol

The highly effective alk-Ti₃C₂/bimetallic Co, Zn embedded N-doped carbon (Co-Zn-NC) composite was fabricated by a convenient self-assembled method strategy and applied to  the reduction of 4-nitrophenol(4-NP). Co-Zn-NC nanocage was synthesized by using designed core-shell ZIF-8@ZIF-67 as sacrificial template. The Co-Zn-NC was prepared by pyrolysis of ZIF-8@ZIF-67 at 900 °C with high-specific surface area and hollow structure, which facilitates the dispersion of Co species and produces abundant Co-Nx active sites. In addition, the electrochemical property and specific surface area of Ti₃C₂ were improved by alkaline treatment. As a result, compared with alk-Ti₃C₂ and Co-Zn-NC, the alk-Ti₃C₂/Co-Zn-NC sensor showed higher activity and stability in detecting 4-NP. The alk-Ti₃C₂/Co-Zn-NC sensor has a wide determination range of 2-500 μM and a low detection limit of 0.23 μM for 4-NP. In addition, the newly developed alk-Ti₃C₂/Co-Zn-NC sensor displayed satisfactory reproducibility and  good stability in detecting 4-NP in aqueous samples.

Synthesis of Nitrogen and Phosphorus/Sulfur Co-Doped Carbon Xerogels for the Efficient Electrocatalytic Reduction of p-Nitrophenol

Carbon xerogels co-doped with nitrogen (N) and phosphorus (P) or sulfur (S) were synthesized and employed as catalysts for the electrocatalytic reduction of p-nitrophenol (p-NP). The materials were prepared by first synthesizing N-doped carbon xerogels (NDCX) via the pyrolysis of organic gels, and then introducing P or S atoms to the NDCX by a vapor deposition method. The materials were characterized by various measurements including X-ray diffraction, N₂ physisorption, Transmission electron microscopy, Fourier Infrared spectrometer, and X-ray photoelectron spectra, which showed that N atoms were successfully doped to the carbon xerogels, and the co-doping of P or S atoms affected the existing status of N atoms. Cyclic voltammetry (CV) scanning manifested that the N and P co-doped materials, i.e., P-NDCX-1.0, was the most suitable catalyst for the reaction, showing an overpotential of -0.569 V (vs. Ag/AgCl) and a peak slop of 695.90 μA/V. The material was also stable in the reaction and only a 14 mV shift in the reduction peak overpotential was observed after running for 100 cycles.

Preparation and Application of Coal-Liquefaction-Residue-Based Carbon Material

P-Nitrophenol (4-NP) is a high toxicity material and has harmful effects on the environment. Thus, the analysis of 4-NP is an important topic at present. In this work, the fabrication of a novel electrochemical sensor based on coal-liquefaction-residue (CLR)-derived porous carbon (PC) materials. CLR-based porous carbon material was prepared by the high-temperature carbonization method and the morphology and structure of the materials were characterized by scanning electron microscopy and other characterization methods. Subsequently, the electrochemical properties of the modified electrodes were studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements. The results showed that under optimal conditions, the sensor had a good electrochemical performance for environmental pollutant 4-NP. In particular, the linear range of the sensor was 10–200 μmol·L-1 and the detection limit was 1.169 μmol·L−1 on the basis of the signal-to-noise ratio S/N = 3. The electrode showed excellent stability, reproducibility and repetitiveness and the sensor also had good selectivity. In addition, the newly constructed sensor exhibited adsorption-controlled kinetics and the recovery rate of 4-NP in actual water samples could reach 90.06~95.17%, indicating that the sensor had good practical application prospects.

AuNPs and graphdiyne nanocomposite as robust electrocatalyst for methyl parathion detection in real samples

The present work describes a simple and rapid synthesis method of gold nanoparticles and graphdiyne (AuNPs@GDY) nanocomposites including porous structure. Moreover, the synthesized AuNPs@GDY material was decorated on the glassy carbon electrode (GCE) with a drop coating method to construct a non-enzymatic electrochemical pesticides sensor. The micro-morphology and elemental composition of the materials were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The electrocatalysis and conductivity of the material were studied with cyclic voltammetry (CV) and impedance method, respectively. The properties of the sensor were investigated by CV and differential pulse voltammetry (DPV). The results showed that AuNPs@GDY exhibited excellent electrocatalytic ability for methyl parathion in a wide linear range (from 0.25 ng/mL to 24.43 μg/mL) and low limit of detection value (6.2 pg/mL). Furthermore, the DPV method used in this paper was accurate and sensitive, and could be used for routine quality control of methyl parathion in kiwi fruit and tomato samples.

Preparation of Graphite-UiO-66(Zr)/Ti electrode for efficient electrochemical oxidation of tetracycline in water

Tetracycline (TC) is widely-used antibiotic pollutant with high toxicity, refractory, persistence and bacteriostasis, and its removal from water needs to be enhanced. In this work, a novel Graphite-UiO-66(Zr)/Ti electrode was successfully prepared and evaluated for electrochemical oxidation degradation of TC. The electrochemical performance tests indicate the Graphite-UiO-66(Zr)/Ti electrode had higher electrochemical oxidation activity, which achieved higher TC removal efficiency (98.1% ± 1.5%) than Ti plate (65.2% ± 3.5%), Graphite-MIL-53(Al)/Ti electrode (79.5% ± 2.9%) and Graphite-MIL-100(Fe)/Ti electrode (89.0% ± 2.6%). The influence of operating condition was also systematically studied, and the optimized condition was pH 5.0, 20 mA/cm2 current density and 0.1 M electrolyte (Na2SO4). Through the liquid chromatography mass spectrometry (LC-MS), the TC degradation pathway by Graphite-UiO-66(Zr)/Ti electrode oxidation was proposed. Under the •OH free radical oxidative decomposition effect, the double bond, phenolic group and amine group of TC were attacked. TC was transformed into intermediate product ① (m/z = 447), then was further degraded to intermediates ② (m/z = 401) and ③ (m/z = 417). The latter was fragmented into small fractions ④ (m/z = 194), ⑤but-2-enedioic acid (m/z = 116) and ⑥oxalic acid (m/z = 90, the proposed intermediate). In addition, TC removal remained at 89.6% ± 2.7% in the sixth cycle of operation, which confirmed the efficient reusability and stability for antibiotics removal from water.

Sensitive electrochemical detection of p-nitrophenol by pre-activated glassy carbon electrode integrated with silica nanochannel array film

Convenient, rapid and sensitive detection of p-nitrophenol (p-NP), one of the priority environmental pollutants, in environmental samples is of great significance. Electrochemical sensor with simple fabrication process, high sensitivity and selectivity, good antifouling, and regeneration performance is highly desirable. Herein, an electrochemical sensing platform is demonstrated based on the integration of vertically-ordered mesoporous silica-nanochannel film (VMSF) on electrochemical pre-activated glassy carbon electrode (p-GCE), which is able to realize ultrasensitive detection of p-NP in environmental samples. Electrochemical pre-activation of GCE is achieved through a simple and green electrochemical polarization process including anodic oxidation at high voltage and the following cathodic reduction at low voltage. The p-GCE possesses enhanced active area and introduced active sites, and enables stable binding of VMSF. VMSF is easily grown on p-GCE through the electrochemically assisted self-assembly (EASA) method within 10 s. Owing to the hydrogen bonding between silanol groups and p-NP, VMSF nanochannels display strong enrichment effect for the detection of p-NP. The developed VMSF/p-GCE sensor can achieve sensitive detection of p-NP ranging from 10 nM to 1 μM and from 1 to 30 μM with a limit of detection (LOD) of 9.4 nM. Considering the antifouling ability of VMSF, detection of p-NP in pond water is achieved.

Rapid removal of chloramphenicol via the synergy of Geobacter and metal oxide nanoparticles

The wide use of chloramphenicol and its residues in the environments are an increasing threat to human beings. Electroactive microorganisms were proven with the ability of biodegradation of chloramphenicol, but the removal rate and efficiency need to be improved. In this study, a model electricigens, Geobacter metallireducens, was supplied with and Fe₃O₄ and MnO₂ nanoparticles. Five times higher chloramphenicol removal rate (0.71 d^-1) and two times higher chloramphenicol removal efficiency (100%) was achieved. Fe₃O₄ and MnO₂ nanoparticles highly increased the current density and NADH-quinone oxidoreductase expression. Fe₃O₄ nanoparticles enhanced the expression of alcohol dehydrogenase and c-type cytochrome, while MnO₂ nanoparticles increased the transcription of pyruvate dehydrogenase and Type IV pili assembly genes. Chloramphenicol was reduced to a type of dichlorination reducing product named CPD3 which is a benzene ring containing compound. Collectively, Fe₃O₄ and MnO₂ nanoparticles increased the chloramphenicol removal capacity in MFCs by enhancing electron transfer efficiency. This study provides new enhancing strategies for the bioremediation of chloramphenicol in the environments.