Hydrogeochemistry and health hazards of fluoride-enriched groundwater in the Tarim Basin, China.

Fluoride (F-) enrichment reduces the availability of groundwater resources in the arid region, and it is thus important to investigate the hydrogeochemistry and health hazards of fluoride-enriched groundwater. Seventy-two groundwater samples (20 unconfined samples from the piedmont plain, 22 unconfined samples and 30 shallow confined samples from the alluvial plain) were collected in the Tarim Basin of China to illustrate the geochemical processes driving the F- enrichment and the incidence of dental fluorosis. The patterns of average ions contents in groundwater are Na+ > Ca2+ > Mg2+ > K+ and SO42- > Cl- > HCO3- > NO3- > F-. The highest F- concentration (average 2.16 mg/L) is observed in unconfined groundwater in the alluvial plain, while the lowest (average 0.63 mg/L) is recorded in unconfined groundwater in the piedmont plain. Approximately 5.0% of unconfined groundwater in the piedmont plain, 90.9% of unconfined groundwater and 33.3% of shallow confined groundwater in the alluvial plain contain F- concentrations exceeding 1.0 mg/L (Chinese drinking water standard). Mineral dissolution, cation exchange, and evaporation play a significant role in the formation of solutes in groundwater. High-F- groundwater is mostly associated with SO4·Cl-Na·Ca, SO4·Cl-Na·Mg, and SO4·Cl-Na types water. Thermodynamic simulations reveal that the dissolution of F-bearing minerals (e.g., fluorite) significantly controls the F- contents in groundwater. High concentrations of F- are closely related to high HCO3-, high Na+, high salinity, cation exchange, and evaporation. This demonstrates that high F- concentrations are caused by the increase in fluorite solubility due to high ionic strength, Ca2+ consumption and the desorption of F- from solid surfaces under alkaline conditions. Mixing with the upper unconfined groundwater plays a vital role in the enrichment of F- in shallow confined groundwater in the alluvial plain. The health risk assessment based on Dean's classification indicates that the percentage prevalence of fluorosis for boys aged 6 to 18 is 15.5% for Yecheng (YC), 18.4% for Zepu (ZP), 33.3% for Shache (SC), 29.8% for Maigaiti (MG), and 44.9% for Bachu (BC), while that for girls of the same age is 14.3% for YC, 24.3% for ZP, 42.2% for SC, 41.4% for MG, and 45.3% for BC. For male and female adults aged between 19 and 68, the percentage prevalence of fluorosis is: YC (11.5%, 12.0%), ZP (18.3%, 20.0%), SC (35.4%, 35.0%), MG (32.5%, 39.7%), and BC (42.4%, 44.3%). It is obvious that younger generation, especially girls, suffers from more severe dental fluorosis. This study has implications for the effective management of high-F- groundwater in arid regions.

Portable electrochemical carbon cloth analysis device for differential pulse anodic stripping voltammetry determination of Pb2.

A novel electrochemical carbon cloth (CC) analysis device (eCAD) is proposed for the determination of Pb2+ in environmental water samples, which was assembled using a single-step functional CC as both the sensing and the substrate material. The modified CC was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectra, and electrochemical impedance spectroscopy. The increase in electrochemical activity is due to the increased defective extent and excellent electrochemical activity of CC. Under optimum conditions (viz. a pH value of 4.5, deposition time of 160 s), the sensor is capable of determining Pb2+ by differential pulse anodic stripping voltammetry (DPASV) at a typical working potential of - 1.0 V (vs. Ag/AgCl). Response is linear from 5.0 × 10-9 to 3.0 × 10-6 M Pb2+, and the detection limit is 4.8 nM (at S/N = 3). The sensor was successfully applied to the determination of Pb2+ in real samples, with apparent recoveries from 96.0 to 102.0% and a relative standard deviation of less than 3.4%. In addition, the integration of the sensor with signal collection components has enabled us to realize on-site analysis of Pb2+, which is highlighted as a new generation of electrode platform for the development of a portable analysis device.Graphical abstract.

Cost-effective mid-infrared micropolarizer fabricated on common silicon by soft nanoimprint lithography.

We fabricated a cost-effective mid-IR micropolarizer on a common Si substrate. To improve the transmittance of Si, we performed a double oxidation on the silicon substrate. The SiO2-Si-SiO2 structure improved the transmittance of Si from 54% to 63%-83%. Then, the mid-IR micropolarizer with multidirectional gratings was fabricated using a soft nanoimprint process followed by the thermal evaporation of Al. Experimental measurements showed a transverse magnetic transmittance in the range of 61%-80% at wavelengths of 4-5 µm, and the extinction ratio was greater than 19 dB.

Infrared micropolarizer array fabricated using a reversal nanoimprint.

Using a reversal nanoimprint and metal evaporation process, we fabricated a micropolarizer array for the 2.5-7 µm wavelength region. The micropolarizer array has a unique unit, which is composed of 2×3 arrays on an intrinsic silicon substrate. Each array consists of a 200 nm period bilayer Al grating in a 1.3 mm×1.3 mm aperture. The transmittance of transverse magnetic polarization of each array is greater than 65% in the 2.5-7 µm wavelength range, and the extinction ratio is over 35 dB in the 3-4 µm and 6-7 µm wavelength range. This fabricated micropolarizer array has lower costs and better compatibility with microfabrication processes.

Large-area flexible infrared nanowire grid polarizer fabricated using nanoimprint lithography.

We fabricated a 4-in large-area flexible infrared nanowire grid polarizer using a nanoimprint and metal thermal evaporation process. To protect the Si master template, as well as to prolong the service life of it, we first fabricated a nickel template as an alternative by an electroforming process. Then, the nanowire grid structure was transferred from this template to IPS substrate by a thermal nanoimprint process. Finally, Al was deposited on the IPS nanowire structure by vertical thermal evaporation technology. The results of the infrared optical test reveal that the TM transmittance of the polarizer is greater than 60% in the 4-5.71 µm and 5.73-6.7 µm wavelength ranges, and, especially, it is greater than 70% in the wavelength ranges of 4.70-5.69 µm and 5.75-6.59 µm. The extinction ratio is more than 20 dB in the wavelength range of 3.6-6.7 µm, proving that the polarizer has good polarization characteristics. The flexible infrared nanowire grid polarizer has potential applications in the fields of curved surface monitoring equipment and polarized imaging equipment.

Visible-IR transmission enhancement through fog using circularly polarized light.

Detection range is an important factor affecting the transmission characteristics of polarized light through fog. We first selected certain spectral bands from visible to IR wavelengths that exhibit lower path loss. For both radiation fog and advection fog, these optimized wavelength ranges include 0.4-1.1 µm, 1.48-1.56 µm, 1.63-1.86 µm, 2.03-2.18 µm, and 2.39-2.45 µm, and radiation fog in particular contains 3.5-4.3 µm. The long-wave IR wavelengths were excluded due to higher absorption losses. We further investigated the transmission performance of circular and linear polarization in variable foggy environments, exploring the impact of the detection range in particular. Using polarization-tracking Monte Carlo simulations for varying particle size, wavelength, refractive index, and detection range, we show that circular polarization outperforms linear polarization when transmitting in both radiation and advection fog. For radiation fog, circular polarization persists longer than linear polarization for 5 µm and 9 µm particles over the entire optimized wavelength range from the visible to mid-wave IR (MWIR). However, linear polarization outperforms circular polarization for 1 µm particles over the entire MWIR and a part of the short-wave IR (SWIR). For advection fog, circular polarization persists longer than linear polarization for all three particle sizes (10, 20, and 40 µm) over the entire optimized wavelength range from the visible to SWIR. We show that circular polarization retains a higher degree of polarization and has better enhancement in some detection ranges.

A Simple and Efficient Magnesium Hydroxide Modification Strategy for Flame-Retardancy Epoxy Resin.

Magnesium hydroxide, as a green inorganic flame-retardancy additive, has been widely used in polymer flame retardancy. However, magnesium hydroxide is difficult to disperse with epoxy resin (EP), and its flame-retardancy performance is poor, so it is difficult to use in flame-retardant epoxy resin. In this study, an efficient magnesium hydroxide-based flame retardant (MH@PPAC) was prepared by surface modification of 2-(diphenyl phosphine) benzoic acid (PPAC) using a simple method. The effect of MH@PPAC on the flame-retardancy properties for epoxy resins was investigated, and the flame-retardancy mechanism was studied. The results show that 5 wt% MH@PPAC can increase the limiting oxygen index for EP from 24.1% to 38.9%, achieving a V-0 rating. At the same time, compared to EP, the peak heat release rate, peak smoke production rate, total smoke production rate, and peak CO generation rate for EP/5 wt% MH@PPAC composite material decreased by 53%, 45%, 51.85%, and 53.13% respectively. The cooperative effect for PPAC and MH promotes the formation of a continuous and dense char layer during the combustion process for the EP-blend material, significantly reducing the exchange for heat and combustible gases, and effectively hindering the combustion process. Additionally, the surface modification of PPAC enhances the dispersion of MH in the EP matrix, endowing EP with superior mechanical properties that meet practical application requirements, thereby expanding the application scope for flame-retardant EP-blend materials.

Fluoride and nitrate contamination of groundwater in the Loess Plateau, China: Sources and related human health risks.

Fluoride (F-) and nitrate (NO3-) in groundwater have caused serious health problems worldwide. However, in the Chinese Loess Plateau where groundwater is the primary source of drinking water, previous studies have rarely reported the health risks from fluoride and nitrate in groundwater. Therefore, we collected 105 groundwater samples (78 from shallow aquifers and 27 from deep aquifers) from the western district of the Loess Plateau for physicochemical and isotopic analysis to investigate the sources of F- and NO3- in groundwater and associated health risks. Fluoride concentration in 73.1% of shallow groundwater and 22.2% of deep groundwater exceeds 1.5 mg/L, while NO3- content in 76.3% of shallow groundwater and 51.9% of deep groundwater surpasses 50 mg/L. High-F- groundwater is associated with HCO3-Na, SO4-Na·Mg and Cl-Na·Mg types water. Fluorine-bearing minerals dissolution, cation exchange, calcite precipitation, evaporation, and anthropogenic activities contribute significantly F- in groundwater. Mixing with shallow groundwater is an important source of F- in deep groundwater. The NO3- content is highest in Cl type water, followed by SO4 type and HCO3 type water. NO3- mainly originates from soil organic nitrogen (SON), chemical fertilizers (CF), and manure and sewage (M&S). Nitrification is the dominant transformation process of nitrogen nutrients in groundwater. The hazard index (HI) values for shallow groundwater are 0.203-9.232 for adults, 0.253-11.522 for teenagers, 0.359-16.322 for children, and 0.507-23.043 for infants, while those for deep groundwater are 0.713-5.813 for adults, 0.890-7.254 for teenagers, 1.261-10.277 for children, and 1.780-14.508 for infants. Approximately 96.2% of shallow groundwater poses non-carcinogenic risks to infants and children, followed by 92.3% to teenagers, and 89.7% to adults. All deep groundwater poses non-carcinogenic risks to infants and children, followed by 92.6% to teenagers, and 74.1% to adults. This study is helpful to develop strategies for the integrated management of high fluoride or nitrate groundwater in arid areas.

Modification of electron structure on the semiconducting single-walled carbon nanotubes for effectively electrosensing guanine and adenine.

The as-prepared SWNTs are always a mixture of metallic (m-) and semiconducting (s-) tubes with quite different electrochemical properties which is a major barrier for their application in many fields. Based on the noncovalent interactions between planar aromatic molecules and SWNTs, the pyrene derivatives 1-docosyloxylmethylpyrene (DomP) was synthesized to separate the m-SWNTs and s-SWNTs via its significant selectivity toward s-SWNTs, i.e. electronic modulation. Before and after doping with electron, the electrochemical properties of s-SWNTs were studied and compared with that of m-SWNTs by electronic absorption spectroscopy, electrochemical impedance spectroscopy and cyclic voltammogram. As demonstrated, the electrocatalytic activity of electron modulated s-SWNTs was significantly improved and even better than m-SWNTs. Thus a novel sensor was constructed with the electron modulated s-SWNTs modified electrode and successfully applied for simultaneous determination of guanine and adenine.