Tungsten-based nanocatalysts with different structures for visible light responsive photocatalytic degradation of bisphenol A.

Environmental pollution, such as water contamination, is a critical issue that must be absolutely addressed. Here, three different morphologies of tungsten-based photocatalysts (WO3 nanorods, WO3/WS2 nanobricks, WO3/WS2 nanorods) are made using a simple hydrothermal method by changing the solvents (H2O, DMF, aqueous HCl solution). The as-prepared nanocatalysts have excellent thermal stability, large porosity, and high hydrophilicity. The results show all materials have good photocatalytic activity in aqueous media, with WO3/WS2 nanorods (NRs) having the best activity in the photodegradation of bisphenol A (BPA) under visible-light irradiation. This may originate from increased migration of charge carriers and effective prevention of electron‒hole recombination in WO3/WS2 NRs, whereby this photocatalyst is able to generate more reactive •OH and •O2- species, leading to greater photocatalytic activity. About 99.6% of BPA is photodegraded within 60 min when using 1.5 g/L WO3/WS2 NRs and 5.0 mg/L BPA at pH 7.0. Additionally, the optimal conditions (pH, catalyst dosage, initial BPA concentration) for WO3/WS2 NRs are also elaborately investigated. These rod-like heterostructures are expressed as potential catalysts with excellent photostability, efficient reusability, and highly active effectivity in different types of water. In particular, the removal efficiency of BPA by WO3/WS2 NRs reduces by only 1.5% after five recycling runs and even reaches 89.1% in contaminated lake water. This study provides promising insights for the nearly complete removal of BPA from wastewater or different water resources, which is advantageous to various applications in environmental remediation.

Adsorptive removal of benzene and toluene from aqueous solutions by oxygen-functionalized multi-walled carbon nanotubes derived from rice husk waste: A comparative study.

One of the current directions for sustainable development is to use waste resources to create materials that reduce environmental pollution. In this study, multi-walled carbon nanotubes (MWCNT) and their oxygen-functionalized forms (HNO3/H2SO4-oxidized MWCNT, NaOCl-oxidized MWCNT, and H2O2-oxidized MWCNT) were first synthesized from activated carbon (AC) derived from rice husk waste. A comprehensive comparison of the morphological and structural properties of these materials was conducted using FT-IR, BET, XRD, SEM, TEM, TGA, Raman spectroscopy, and surface charge analysis. The morphology study suggests that the synthesized MWCNTs have an average outer and inner diameter of about 40 and 20 nm, respectively. Additionally, the NaOCl-oxidized MWCNT possesses the largest interspaces between nanotubes, while the HNO3/H2SO4-oxidized CNT has the most oxygen-functional groups, including -COOH, (Ar)-OH, and C-OH. The adsorption capacities of these materials were also compared for the removal of benzene and toluene. Experimental results have shown that while porosity is the primary factor governing the benzene and toluene adsorption onto AC, functionalization degree and surface chemical characteristics are the determining factors in the adsorption capacity of the as-prepared MWCNTs. The adsorption capacity of these aromatic compounds in an aqueous solution increases in the following order: AC < MWCNT < HNO3/H2SO4-oxidized MWCNT < H2O2-oxidized MWCNT < NaOCl-oxidized MWCNT, and in all cases, toluene is more readily adsorbed than benzene under similar adsorption conditions. Wherein the uptake of both pollutants by the prepared adsorbents in this study is best described by the Langmuir isotherm and obeys the pseudo-second-order kinetic model. The adsorption mechanism was discussed in a detailed manner.

Mapping potential conflicts between global agriculture and terrestrial conservation.

Demand for food products, often from international trade, has brought agricultural land use into direct competition with biodiversity. Where these potential conflicts occur and which consumers are responsible is poorly understood. By combining conservation priority (CP) maps with agricultural trade data, we estimate current potential conservation risk hotspots driven by 197 countries across 48 agricultural products. Globally, a third of agricultural production occurs in sites of high CP (CP > 0.75, max = 1.0). While cattle, maize, rice, and soybean pose the greatest threat to very high-CP sites, other low-conservation risk products (e.g., sugar beet, pearl millet, and sunflower) currently are less likely to be grown in sites of agriculture-conservation conflict. Our analysis suggests that a commodity can cause dissimilar conservation threats in different production regions. Accordingly, some of the conservation risks posed by different countries depend on their demand and sourcing patterns of agricultural commodities. Our spatial analyses identify potential hotspots of competition between agriculture and high-conservation value sites (i.e., 0.5° resolution, or ~367 to 3,077km2, grid cells containing both agriculture and high-biodiversity priority habitat), thereby providing additional information that could help prioritize conservation activities and safeguard biodiversity in individual countries and globally. A web-based GIS tool at https://agriculture.spatialfootprint.com/biodiversity/ systematically visualizes the results of our analyses.

Kinetic study on methylene blue removal from aqueous solution using UV/chlorine process and its combination with other advanced oxidation processes.

This study investigated the kinetic degradation of methylene blue (MB) by a UV/chlorine process and its combination with other advanced oxidation processes. The ∙OH and reactive chlorine species (RCS: Cl∙, ClO∙, etc.) were the primary reactive species, which accounted for 56.7% and 37.6% of MB degradation at pH 7, respectively. The second-order rate constant of Cl∙ towards MB was calculated to be 2.8 × 109 M-1 s-1. When the pH increased from 3 to 7, kMB by ∙OH increased from 0.15 to 0.21 min-1 before being reduced to 0.11 min-1 at pH 11. kMB by RCS continuously reduced from 0.16 to 0.13 min-1 when the pH was increased to 11. Humic acid (HA), Br-, and Cl- inhibited the degradation with kMB in the order: kMB (in HA) < kMB (in Br-) < kMB (in Cl-). HCO3- increased kMB from 0.37 to 0.48 min-1. The experimental and modeling methods fit well, indicating the effectiveness of using Kintecus® in predicting concentrations of free radicals in complex water matrices. TOC removal was achieved at 60% after 30 min in a control process and it was strongly inhibited by the presence of HA, with 22% removal achieved at 5 mgc L-1 HA. UV/chlorine/electrochemical oxidation (UV/chlorine/EO) significantly improves kMB from 0.37 to 0.94 min-1 at a high current (240 mA), while UV/chlorine/H2O2 decreased kMB at a low concentration of 0.01 mM H2O2 (kMB decreased by 6.1%). The results indicate that the energy cost for UV irradiation was the main cost in MB treatment in both UV/chlorine and UV/persulfate (UV/PS) processes, accounting for 91% and 84%, respectively.

Electrochemical preparation of monodisperse Pt nanoparticles on a grafted 4-aminothiophenol supporting layer for improving the MOR reaction.

The methanol oxidation reaction (MOR) has recently gained a lot of attention due to its application in fuel cells and electrochemical sensors. To enhance the MOR, noble metal nanoparticles should be homogeneously dispersed on the electrode surface with the aid of one suitable support. In this work, 4-aminothiophenol (4-ATP) molecules which contain simultaneously amine and thiol groups were electro-grafted onto the electrode surface to provide anchoring sites, limit aggregation and ensure good dispersion of metal nanoparticles. The results showed a high density of platinum nanoparticles (PtNPs) with an average size of 25 nm on the glassy electrode modified with a 4-ATP supporting layer. Consequently, the MOR was improved by 2.1 times with the aid of the grafted 4-ATP layer. The electrochemical sensor based on PtNPs/4-ATP/GCE is able to detect MeOH in a linear range from 1.26 to 21.42 mM with a detection limit of 1.21 mM.

Degradation of dyes by UV/Persulfate and comparison with other UV-based advanced oxidation processes: Kinetics and role of radicals.

This study investigated the degradation of methylene blue (MeB), methyl orange (MeO), and rhodamin B (RhB) by the UV/Persulfate (UV/PS) process. The dye degradation in the investigated UV-based Advanced Oxidation Processes (UV/AOPs) followed the first-order kinetic model. The second-order rate constant of the dyes with •OH, SO4•-, and CO3•- were calculated and found to be: k•OH,MeB = 5.6 × 109 M-1 s-1, [Formula: see text]  = 3.3 × 109 M-1 s-1, [Formula: see text]  = 6.9 × 107 M-1 s-1; k•OH,MeO = 3.2 × 109 M-1 s-1, [Formula: see text]  = 13 × 109 M-1 s-1, [Formula: see text]  = 4.4 × 106 M-1 s-1; k•OH,RhB = 14.8 × 109 M-1 s-1, [Formula: see text]  = 5 × 109 M-1 s-1, [Formula: see text]  = 1 × 107 M-1 s-1. The steady-state concentrations of •OH and SO4•- (including other reactive species) were determined using both chemical probes and modeling methods (Kintecus® V6.8). In the UV/PS, the dye degradation depends on the pH of the solution with the order: kdye (at pH of 7) > kdye (in acidic conditions) > kdye (in alkaline conditions). The presence of water matrices had different impacts on dye degradation: 1) The HCO3- and Cl- promoted the degradation efficiency of one dye, but also inhibited the degradation of other dyes; 2) Humic acid (HA) inhibited dye degradation as it scavenged both •OH and SO4•-. The degradation of the dyes by UV/PS was also compared with the UV/Chlorine (UV/HOCl) and UV/H2O2 and it was established that: 1) In UV/PS and UV/HOCl, SO4•- and RCS contributed to dye degradation more than •OH, while •OH played a major role in dye degradation by UV/H2O2; 2) The calculated toxicity in UV/PS was the lowest probably due to the low toxicity of by-products; 3) For MeO and RhB, the UV/PS process is more beneficial for the total organic carbon (TOC) removal compared to that of the UV/HOCl and UV/H2O2 processes; 4) The UV/PS showed lower cost than the UV/HOCl and UV/H2O2 systems for MeO, and RhB degradation but higher cost for MeB removal.

Insight into electrochemical degradation of Cartap (in Padan 95SP) by boron-doped diamond electrode: kinetic and effect of water matrices.

In this work, the kinetic electrochemical degradation of Cartap (CT) (in Padan 95 SP) at boron-doped diamond (BDD) electrode was investigated. This study indicated that the degradation of CT underwent both direct and indirect oxidations. Water matrices can either accelerate or inhibit the removal efficiency of CT: adding 15 mM Cl- improved kCT from 0.039 min-1 to 0.054 min-1 (increased by 38%), while kCT decreased by 61.5% and 64% when increasing the concentration of HCO3- and humic acid (HA) to 15 mM and 15 mg L-1, respectively. CT degradation was inhibited in the presence of methanol (MeOH) and tert-butanol (TBA) due to the scavenging effect of those chemicals toward reactive species. The contribution of reactive oxidants was calculated as: DET (direct electron transfer) accounted for 15%; •OH accounted for 61.5%; SO4•- accounted for 12.8%; ROS (the other reactive oxygen species) accounted for 8.5%. The transformation pathways of major reactive species were established.

Mapping the deforestation footprint of nations reveals growing threat to tropical forests.

Deforestation, a significant threat to biodiversity, is accelerated by global demand for commodities. Although prior literature has linked deforestation to global supply chains, here we provide a fine-scale representation of spatial patterns of deforestation associated with international trade. Using remote sensing data and a multi-region input-output model, we quantify and map the spatiotemporal changes in global deforestation footprints over 15 years (2001-2015) at a 30-m resolution. We find that, while many developed countries, China and India have obtained net forest gains domestically, they have also increased the deforestation embodied in their imports, of which tropical forests are the most threatened biome. Consumption patterns of G7 countries drive an average loss of 3.9 trees per person per year. Some of the hotspots of deforestation embodied in international trade are also biodiversity hotspots, such as in Southeast Asia, Madagascar, Liberia, Central America and the Amazonian rainforest. Our results emphasize the need to reform zero-deforestation policies through strong transnational efforts and by improving supply chain transparency, public-private engagement and financial support for the tropics.

An Electrochemical Sensor Based on Gold Nanodendrite/Surfactant Modified Electrode for Bisphenol A Detection.

In the present work, we reported the simple way to fabricate an electrochemical sensing platform to detect Bisphenol A (BPA) using galvanostatic deposition of Au on a glassy carbon electrode covered by cetyltrimethylammonium bromide (CTAB). This material (CTAB) enhances the sensitivity of electrochemical sensors with respect to the detection of BPA. The electrochemical response of the modified GCE to BPA was investigated by cyclic voltammetry and differential pulse voltammetry. The results displayed a low detection limit (22 nm) and a linear range from 0.025 to 10 µm along side with high reproducibility (RSD = 4.9% for seven independent sensors). Importantly, the prepared sensors were selective enough against interferences with other pollutants in the same electrochemical window. Notably, the presented sensors have already proven their ability in detecting BPA in real plastic water drinking bottle samples with high accuracy (recovery range = 96.60%-102.82%) and it is in good agreement with fluorescence measurements.

Effects of nutrient supply and nutrient ratio on diversity-productivity relationships of phytoplankton in the Cau Hai lagoon, Vietnam.

Diversity and productivity of primary producers are known to be influenced simultaneously by resource availability and resource ratio, but the relative importance of these two factors differed among studies and so far only entire phytoplankton communities were investigated which might ignore specific nutrient requirements and stoichiometric plasticity of different functional groups. We measured nutrient availability (DIN, total N [TN], total P [TP]), nutrient imbalance (TN:TP, DIN:TP, N:Pseston), species richness, and abundance of the whole phytoplankton community, as well as those specific for cyanobacteria, diatoms, and dinoflagellates in Cau Hai lagoon in Vietnam. We determined the correlation among these variables, using structural equation modeling. The models applied to the whole phytoplankton community indicated that the nutrient availability (particularly TP and DIN) drove variation in phytoplankton abundance and richness, and that abundance also depended on species richness. The models applied to different functional groups differed considerably from the entire community and among each other, and only a part of the models was significant. The relationship between nutrient availability (mainly TP) and abundance was driven by cyanobacteria, and the relationship between nutrient imbalance (only with N:Pseston) and species richness was driven by diatoms. Remarkably, the positive relationship between species richness and abundance, as consistently observed for the whole phytoplankton community, was only observed for one of the three functional groups (diatoms), indicating that resource complementarity occurs particularly among species of different functional groups. Our results emphasized that nutrient availability (TP and to a lesser extent DIN) as well as nutrient imbalance (albeit only with N:Pseston as proxy) were driving factors for the phytoplankton community in the Cau Hai lagoon and hence alterations in both of these factors leading to a shift in phytoplankton species composition and productivity.