Investigation on redox mechanism of p-aminophenol in non-aqueous media by FT-IR spectroelectrochemistry

Iron content in aerosol particles and its impact on atmospheric chemistry

Atmospheric aerosol effects on ecological and human health remain uncertain due to their highly complex and evolving nature when suspended in air. Atmospheric chemistry, global climate/oceanic and health exposure models need to incorporate more realistic representations of aerosol particles, especially their bulk and surface chemistry, to account for the evolution in aerosol physicochemical properties with time. (Photo)chemistry driven by iron (Fe) in atmospheric aerosol particles from natural and anthropogenic sources remains limited in these models, particularly under aerosol liquid water conditions. In this feature article, recent advances from our work on Fe (photo)reactivity in multicomponent aerosol systems are highlighted. More specifically, reactions of soluble Fe with aqueous extracts of biomass burning organic aerosols and proxies of humic like substances leading to brown carbon formation are presented. Some of these reactions produced nitrogen-containing gaseous and condensed phase products. For comparison, results from these bulk aqueous phase chemical studies were compared to those from heterogeneous reactions simulating atmospheric aging of Fe-containing reference materials. These materials include Arizona test dust (AZTD) and combustion fly ash particles. Also, dissolution of Fe and other trace elements is presented from simulated human exposure experiments to highlight the impact of aerosol aging on levels of trace metals. The impacts of these chemical reactions on aerosol optical, hygroscopic and morphological properties are also emphasized in light of their importance to aerosol-radiation and aerosol-cloud interactions, in addition to biogeochemical processes at the sea/ocean surface microlayer upon deposition. Future directions for laboratory studies on Fe-driven multiphase chemistry are proposed to advance knowledge and encourage collaborations for efficient utilization of expertise and resources among climate, ocean and health scientific communities.

A highly sensitive method for the detection of p-Aminophenol based on Cu-Au nanoparticles and KIO3

BACKGROUND

As a common industrial raw material and chemical intermediate, p-Aminophenol (pAP) is recognized as a serious pollutant that poses harm to both the environment and human health. The traditional detection methods for pAP have the advantages of good selectivity and high sensitivity, but their complex operation and time-consuming defects limit their application in on-site detection. Therefore, it is necessary to develop a simple, low-cost, rapid and high-sensitivity method for the detection of pAP.

RESULTS

Noble metal nanoparticles have been widely used in colorimetric sensing because of their simplicity and practicality. Herein, we presented a simple, excellent sensitive and selective colorimetric method for high-performance detection of pAP based on Cu-Au nanoparticles (Cu-Au NPs) and KIO3. In the presence of pAP, KIO3 was reduced to I2, which subsequently chemically adsorbed onto Cu-Au NPs surface and induced the dispersion and reorganization of Cu-Au NPs, along with prominent color change of the dispersion from gray-blue to pink and the transformation of Cu-Au NPs from chain-like aggregates to individual dispersed, irregular, subspherical nanoparticles. The mechanism was verified by TEM, DLS, Zeta potential, UV-vis and XPS. Meanwhile, Cu-Au NPs probe can rapidly detect pAP within 25 min, the limit of detection of pAP probe is 5 μM by the naked eyes and 0.03 μM by UV-vis absorption spectrum.

SIGNIFICANCE AND NOVELTY

This is the first colorimetric assay for pAP based on Cu-Au NPs probe. The satisfactory linearity (R2 = 0.9984) indicates that the colorimetric probe based on Cu-Au NPs and KIO3 can be utilized for quantitative detection of pAP. The detection results of pAP in real environmental water samples, urine samples and paracetamol tables demonstrate the practicability of pAP colorimetric probe.

A novel sensor based on Ti3C2 MXene/Co3O4/carbon nanofibers composite for the sensitive detection of 4-aminophenol

A novel, sensitive Ti3C2 MXene/Co3O4/carbon nanofibers (Ti3C2 MXene/Co3O4/CNFs) composite was synthesized via a HF exfoliating Ti3AlC2 strategy, followed by doping Co3O4 and Ti3C2 MXene into the CNFs via a combination electrospinning and thermal annealing process. Ti3C2 MXene/Co3O4/CNFs composite exhibits higher catalytic effect, conductivity, chemical stability, and electrochemical performance than Co3O4 and Ti3C2 MXene in electrochemical impedance, differential pulse stripping voltammetry, chronocoulometry, and cyclic voltammetry tests. This Ti3C2 MXene/Co3O4/CNFs hybrid modified electrode provides fast analysis of 4-aminophenol (4-AP) with ultrahigh sensitivity, enhanced reproducibility and strong anti-interference capability. Furthermore, the level of 4-AP was quantified by this electrode with a wide linear range from 0.5 to 150 μM (R2 > 0.99) and a low detection limit about 0.018 μM was achieved. Finally, the fabricated electrode was used for fast and sensitive analysis of 4-AP spiked in tap water and blood serum samples. This work presents the new Ti3C2 MXene/Co3O4/CNFs electrode provides a platform for 4-AP monitoring and has the advantages of high selectivity, accuracy, simplicity, and rapid analysis.

Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization of o- and p-aminophenols under simulated aerosol and cloud conditions (pH 1-7, and ionic strength 0.01-1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4-0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products of o- and p-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions.

Adsorption and Electropolymerization of p-Aminophenol Reduces Reproducibility of Electrochemical Immunoassays

This paper investigates the electrochemical behavior of p-aminophenol (PAP) on commercially available carbon screen-printed electrodes (CSPEs) and gold screen-printed electrodes (GSPEs) at neutral and basic pHs for the development of inexpensive immunoassays. The electrochemical oxidative signal from PAP results from its adsorption to the electrode. The formation of self-assembled monolayers on gold electrodes prevented PAP adsorption but also reduced its oxidative current, confirming that adsorption increases signal production. On bare electrodes, PAP adsorption results in oxidative current variability depending on the electroactive surface area of the screen-printed electrode. This variability could not be remedied by cleaning and reusing the same GSPE. Decreasing the PAP concentration to 3.8 μM greatly improved the consistency of the measurements, suggesting that the adsorption of PAP is concentration-dependent. Multiple PAP oxidations on the same electrode caused polymerization, limiting PAP in continuous monitoring applications. Infrared and Raman spectroscopy allow the distinction between adsorbed PAP and electropolymerized PAP on the surface of a gold wafer. The results from this study suggest that the use of PAP production in immunoassays with SPEs must be fine-tuned, and electrodes must be cleaned or disposed of between measurements.

Coupled biodegradation of p-nitrophenol and p-aminophenol in bioelectrochemical system: Mechanism and microbial functional diversity

Biodegradation mechanisms and microbial functional diversity during coupled p-nitrophenol (PNP) and p-aminophenol (PAP) degradation were studied in a bioelectrochemical system. PNP in the biocathode and PAP in the bioanode were almost completely removed within 28hr and 68hr respectively. The degradation followed the steps including hydrating hydroxyalkylation, dehydrogenating carbonylation, and hydrolating ring cleavage, etc. Metagemomic analysis based on the KEGG and eggNOG database annotations revealed the microbial composition and functional genes/enzymes related to phenol degradation in the system. The predominant bacteria genera were Lautropia, Pandoraea, Thiobacillus, Ignavibacterium, Truepera and Hyphomicrobium. The recognized biodegradation genes/enzymes related to pollutant degradation were as follows: pmo, hbd, & ppo for phenol degradation, nzba, amie, & badh for aromatic degradation, and CYP & p450 for xenobiotics degradation, etc. The co-occurrence of ARGs (antibiotic resistant genes), such as adeF, MexJ, ErmF, PDC-93 and Escherichia_coli_mdfA, etc., were annotated in CARD database during the biodegradation process. The Proteobacteria & Actinobacteria phylum was the primary host of both the biodegradation genes & ARGs in this system. The microbial functional diversity ensured the effective biodegradation of the phenol pollutants in the bioelectrochemical system.

Experimental and Theoretical Study on the Interaction of P-Aminophenol Hydrochloride with H2O

UV-Vis absorption spectra, cyclic voltammetry and 1H nuclear magnetic resonance (1H NMR) spectra were applied to explore the hydrogen bond interactions of p-aminophenol hydrochloride (PAH) with H2O. The results indicated the hydrogen bonds were formed in PAH–H2O system. The anodic/cathodic peak potentials and UV-Vis absorption bands of PAH in H2O could be affected due to the interactions. The results of density functional theory, atoms in molecules theory and natural bond orbital analyses further confirmed the existence of hydrogen bonds between the phenolic hydroxyl, –NH3 + protons and Cl− of PAH and H2O. Furthermore, the π-π stacking was suggested between PAH benzene rings from the 1H NMR spectra at higher concentrations.

Facile preparation of Ag/Ni(OH)2 composites with enhanced catalytic activity for reduction of 4-nitrophenol

Preparation and formation mechanism of Ag/Ni(OH)₂ composites with enhanced catalytic activity for reduction of 4-nitrophenol were systematically studied.

Protein-Repellence PES Membranes Using Bio-grafting of Ortho-aminophenol

Surface modification becomes an effective tool for improvement of both flux and selectivity of membrane by reducing the adsorption of the components of the fluid used onto its surface. A successful green modification of poly(ethersulfone) (PES) membranes using ortho-aminophenol (2-AP) modifier and laccase enzyme biocatalyst under very flexible conditions is presented in this paper. The modified PES membranes were evaluated using many techniques including total color change, pure water flux, and protein repellence that were related to the gravimetric grafting yield. In addition, static water contact angle on laminated PES layers were determined. Blank and modified commercial membranes (surface and cross-section) and laminated PES layers (surface) were imaged by scanning electron microscope (SEM) and scanning probe microscope (SPM) to illustrate the formed modifying poly(2-aminophenol) layer(s). This green modification resulted in an improvement of both membrane flux and protein repellence, up to 15.4% and 81.27%, respectively, relative to the blank membrane.