Metal loadings in estuarine bivalve and gastropod shellfish in response to socioeconomic development in watershed.

Metal contamination in estuary was monitored globally using shellfish while estuarine metal loadings were influenced by socioeconomic development in watershed, i.e., a watershed-estuary chain effect. Socioeconomic pattern of metal loadings in estuarine shellfish has scarcely been studied. Eight metals and metalloids (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) highly associated with anthropogenic activities were quantified in tissue and shell of bivalves and gastropods (two feeding-habits) among 7 estuaries along the Southeastern China coast in the period 2016-2019. Results indicated that Cu and Zn in shellfish had the greatest loadings at 1,663 and 6,828 mg kg-1 dry mass in tissue and 387 and 151 mg kg-1 dry mass in shell, respectively, in the most developed Estuary Yong. Metal loadings in tissue and shell of bivalves (6 common species) and gastropods (3 common species) in the estuaries were highly associated with urbanization and socioeconomic indicators in their watersheds. The socioeconomic patterns had evident shellfish class-specification and metal-dependency due to the feeding-habit. The class-specification was confirmed by the fractionation of stable isotope compositions for the socioeconomic pattern of Pb loadings in both tissue and shell. In short, both shellfish class-specification and metal-dependency hinted that multi-bioindicators might be required for a comprehensive understanding of the estuarine environment quality, in particular at two dimensions of water and sediment.

Construction of a turn off-on fluorescent nanosensor for cholesterol based on fluorescence resonance energy transfer and competitive host-guest recognition.

Using chloroauric acid as precursor and ß-cyclodextrin (ß-CD) as reducing agent and stabilizer, ß-CD@AuNPs with negative charge were synthesized by one-step colloidal synthesis method. The positive charged carbon quantum dots (CQDs) were synthesized by one-step of sonication of cetylpyridinium chloride. Under the role of static electricity, the fluorescence resonance energy transfer (FRET) occurred between CQDs and ß-CD@AuNPs. CQDs and ß-CD@AuNPs served as the fluorescence energy donors and receptors, respectively, i.e., the fluorescence of CQDs was turned off by ß-CD@AuNPs. Based on the specific host-guest recognition between the inner cavity of ß-CD and cholesterol, CQDs was replaced by cholesterol, the FRET could be interrupted, and then the fluorescence of CQDs was turned on. A good linear relationship between cholesterol concentration (10-210 µmol L-1) and fluorescence intensity was obtained and the LOD was 343.48 nmol L-1. Because of excellent fluorescence quenching ability of FRET, the analytical performance (including LOD and linear scope) of such a turn off-on fluorescent nanosensor (e.g., CQDs/ß-CD@AuNPs) was better than nanosensor only via competitive host-guest recognition (e.g., ß-CD functionalized CQDs). The synergistic effect of competitive host-guest recognition and FRET was proved. Because of selective recognition, ultrasensitive, wide linear range, and strong anti-interference ability, CQDs/ß-CD@AuNPs as a turn off-on fluorescent nanosensor was developed to determine cholesterol in porcine serum.

In situ construction of hollow carbon spheres with N, Co, and Fe co-doping as electrochemical sensors for simultaneous determination of dihydroxybenzene isomers.

Control of the active sites/centers plays an important role in the design of novel electrode materials with unusual properties and achievement of sensors with high performance. In this study, three-dimensional (3D) freestanding multi-doped hollow carbon spheres (N-Co-Fe-HCS) with a layer thickness of 30 nm, which contained multiple active sites of the heteroatom N and transition metals (Co and Fe), were synthesized via a simple template method (with SiO2 as the template) and cost-efficient in situ self-polymerization, self-adsorption/reduction and carbonization strategies. Moreover, a series of hollow carbon sphere composites of the same family (N-HCS, N-Co-HCS and N-Fe-HCS) were prepared by this sensible process using the same method and precursors but different doping elements. These differences lead to different active sites/centers from hollow carbon spheres and improved electrocatalytic activities for dihydroxybenzene isomers. Furthermore, N-Co-Fe-HCS as an electrochemical sensor exhibited excellent simultaneous qualitative and quantitative determination performance for catechol (CC) and hydroquinone (HQ). The detection limit and the linear range were 75 nmol L-1 and 0.5-500 µmol L-1 for CC and 80 nmol L-1 and 0.5-1500 µmol L-1 for HQ, respectively. The interference from the components coexisting in river water on the detection of CC and HQ was not observed. These results indicate that high-performance electrochemical sensors can be constructed by in situ multi-element doping into electrode materials to achieve multi-active sites.

Highly crystalline graphitic carbon nitride quantum dots as a fluorescent probe for detection of Fe(III) via an innner filter effect.

Bulk g-C3N4 was transformed into water-soluble graphitic carbon nitride quantum dots (g-CNQDs) via a chemical oxidation and liquid exfoliation process. The g-CNQDs possess a size distribution ranging from 1 to 5 nm (centered at 3 nm), excellent crystallinity, and are water soluble. It is found that Fe(III) ions are adsorbed on the surface of the g-CNQDs via electrostatic interaction, and that the blue fluorescence of the g-CNQDs is reduced by Fe(III) via an inner filter effect. By using the g-CNQDs as a fluorescent probe, Fe(III) can be determined at excitation/emission wavelengths of 241/368 nm in spiked natural water samples within 1 min and with good selectivity over other ions. Response is linear in the 0.2-60 µmol·L-1 Fe(III) concentration range, and the detection limit is 23 nmol·L-1. Graphical abstract Graphitic carbon nitride quantum dots (g-CNQDs) emit blue fluorescence at an excitation wavelength of 241 nm. Fe(III) ions are quickly adsorbed on the g-CNQDs via electrostatic interaction, and fluorescence is quenched due to an inner filter effect.

A scalable ultrasonic-assisted and foaming combination method preparation polyvinyl alcohol/phytic acid polymer sponge with thermal stability and conductive capability.

In this article, polyvinyl alcohol/phytic acid polymer (PVA/PA polymer) is synthesized from PVA and PA via the esterification reaction of PVA and PA in the case of acidity and ultrasound irradiation, and PVA/PA polymer sponge is prepared via foaming PVA/PA polymer in the presence of n-pentane and ammonium bicarbonate, and the structure of PVA/PA polymer and the structure, morphology and crystallinity of PVA/PA polymer sponge are characterized, and the thermal stability and surface resistivity of PVA/PA polymer sponge are investigated. Based on these, it has been attested that PVA/PA polymer synthesized under the acidity and ultrasound irradiation and PVA/PA polymer sponge are structured by the chain of PVA and the cricoid PA connected in the form of ether bonds and phosphonate bonds, and the thermal stability of PVA/PA polymer sponge attains 416.5 °C, and the surface resistivity of PVA/PA polymer sponge reaches 5.76 × 104 ohms/sq.

Ultrasonic-microwave assisted synthesis of three-dimensional polyvinyl alcohol carbonate/graphene oxide sponge and studies of surface resistivity and thermal stability.

In the article, graphene oxide (GO) was prepared by flake graphite, nitric acid and peroxyacetic acid via the sonochemical method and characterized, and polyvinyl alcohol carbonate/GO composite (PVAC/GO composite) was synthesized by polyvinyl alcohol (PVA), dimethyl carbonate (DMC) and GO via the approach of transesterification in the case of ultrasonic-microwave synergistic effects and characterized, and three-dimensional PVAC/GO sponge (3D PVAC/GO sponge) was manufactured by PVAC/GO composite via the foaming approach and characterized, and the thermal stability and surface resistivity of 3D PVAC/GO sponge were investigated. Based on those, it had been attested that PVAC polymer was structured by DMC and PVA and had the six-membered lactone rings and the ether bonds, and PVAC/GO composite was constituted by 2D GO lattice and PVAC polymer, and 3D PVAC/GO sponge was constructed by PVAC/GO composite, and the surface resistivity of 3D PVAC/GO sponge with 0.00, 0.60, 1.20, 1.80 and 2.40 g of GO were 9.07  ×  107, 6.02  ×  107, 4.65  ×  107, 2.47  ×  107 and 1.06  ×  107 O/sq, and the thermal stability of 3D PVAC/GO sponge had improved.

Constituting fully integrated colorimetric analysis system for Fe(III) on multifunctional nitrogen-doped MoO3/cellulose paper.

Using ammonium molybdate and thiourea as precursors, nitrogen-doped MoO3 was produced by a one-step carbonization and then fixed into the cellulose filter paper (NMCP) with acrylic resin as a fixative. NMCP was designed as a multifunctional nanocomposite, i.e., solid phase adsorbent for Fe(III) preconcentration, photocatalyst for iron species transformation and color interference removal, and colorimetric sensor for Fe(III) determination. After photocatalysis, the complex of Fe-humic substances could be transformed into Fe(III) ions, the interference of colored organic matter (e.g., aqueous humic substance) was removed, Fe(III) was enriched selectively onto NMCP with the coexistence of interference metal ions (e.g. Co(II) and Cd(II)) and then transformed into Fe(II) by hydroxylamine and photoreduction and for colorimetric analysis. The obstacle of o-phenanthroline colorimetric method was overcome. The photodegradation activity of MoO3 was improved 2.02 times by nitrogen doping with the optimal mass ratio, which was also 5.11 times of P25-TiO2. The concentration of Fe(III) on NMCP was quantified by the gray-scale using smart phones and image processing software, without complicated equipment. Based on multifunctional NMCP, a fully integrated visual analysis system was proposed and suitable for the field detection of Fe(III) in natural water. The log-linear calibration curve for Fe(III) was in the range of 0.05-5mg/L with a determination coefficient (R2) of 0.976 and detection limit of 15µg/L.

Noble metal sandwich-like TiO2@Pt@C3N4 hollow spheres enhance photocatalytic performance.

The goal of this work was to assess the performance of Pt nanoparticles (NPs) as co-catalysts on the photocatalytic activity of TiO2@Pt@C3N4 hollow spheres, which was tested by photodegrading rhodamine B and methyl blue under visible light irradiation. TiO2@Pt@C3N4 composites were fabricated by using modified polystyrene balls as templates, hydrothermal reactions, and calcination. Under simulated sunlight irradiation, photocatalytic activity was in the following of TiO2@Pt@C3N4 > TiO2@C3N4 > C3N4 > P25. The photo-conversion rate of the TiO2@Pt@C3N4 increased significantly relative to TiO2@C3N4 and the others. The combination of TiO2 and C3N4, as well as the sandwiched of Pt NPs reduce electron-hole recombination as a result of having an electron trap site, which can store and shuttle photo-generated electrons, and enhance photo-generation of active radicals. Electron paramagnetic resonance (EPR) spectroscopy, as well as photo-luminescence (PL), and electrochemical measurements were taken to verify this conclusion. Considering the multi-functional combination of precious metals and semiconductor materials, this work may provide new ideas for the design of high-performance catalysts.

TiO2@Pt@CeO2 nanocomposite as a bifunctional catalyst for enhancing photo-reduction of Cr (VI) and photo-oxidation of benzyl alcohol.

An solar-light-driven and bifunctional photocatalyst was designed for photo-reduction of Cr(VI) and selective photo-oxidation of benzyl alcohol into benzaldehyde in the presence of water under ambient conditions. Double-shelled and sandwiched TiO2@Pt@CeO2 hollow spheres were prepared by using functionalized polystyrene spheres, sol-gel, hydrothermal reaction, and calcination. The Pt nanoparticles (NPs) were controllably loaded between the TiO2 shell and CeO2 shell. Under solar-light irradiation, the photo-reduction rate of Cr(VI) (µmol h-1) was in the order of TiO2@Pt@CeO2 (1.901) > TiO2@CeO2 (1.424) > TiO2 (1.040) > CeO2 (0.992). Among the above-mentioned photocatalysts, the conversion rate of benzyl alcohol for TiO2@Pt@CeO2 was also the best. These results were attributed to the combination of TiO2 and CeO2 as photocatalyst and oxygen buffer, the double-shelled and sandwiched nanostructure, and the addition of Pt NPs as cocatalyst and electron trap site, which could store and shuttle photo-generated electrons, reduce the recombination of the electron-hole, and then enhance photo-generation of active radicals. This conclusion was verified by the electron paramagnetic resonance (EPR) spectroscopy. Considering the versatile combination of photocatalyst, oxygen buffer and cocatalyst, this work could provide new insights into the design of high-performance bifunctional photocatalysts for heavy metal removal and selective synthesis.

Ultrasonic-assisted preparation of graphene oxide carboxylic acid polyvinyl alcohol polymer film and studies of thermal stability and surface resistivity.

In this paper, flake graphite, nitric acid and acetic anhydride are used to prepare graphene oxide carboxylic acid (GO-COOH) via an ultrasonic-assisted method, and GO-COOH and polyvinyl alcohol polymer (PVA) are used to synthesize graphene oxide carboxylic acid polyvinyl alcohol polymer (GO-COOPVA) via the ultrasonic-assisted method, and GO-COOPVA is used to manufacture graphene oxide carboxylic acid polyvinyl alcohol polymer film (GO-COOPVA film) via a solidification method, and the structure and morphology of GO-COOH, GO-COOPVA and GO-COOPVA film are characterized, and the thermal stability and surface resistivity are measured in the case of the different amount of GO-COOH. Based on the characterization and measurement, it has been successively confirmed and attested that carboxyl groups implant on 2D lattice of GO to form GO-COOH, and GO-COOH and PVA have the esterification reaction to produce GO-COOPVA, and GO-COOPVA consists of 2D lattice of GO-COOH and the chain of PVA connected in the form of carboxylic ester, and GO-COOPVA film is composed of GO-COOPVA, and the thermal stability of GO-COOPVA film obviously improves in comparison with PVA film, and the surface resistivity of GO-COOPVA film clearly decreases.