A high-performance trace level acetone sensor using an indispensable V4C3T x MXene.

The development of a stringent sensor to detect low levels of acetone, yielding the potential for the point-of-care clinical diagnosis of diabetes, is still a great challenge but is urgently required. Most studies have focused on Ti3C2T x , yet other types of MXenes with good performance are rare. Herein, an emerging kind of MXene, V4C3T x , has been prepared from V4AlC3 via the selective etching of the Al layer using aqueous HF at room temperature (RT), and its performance as an acetone sensor is presented. A V4C3T x based acetone sensor delivers good performance, as demonstrated by its low working temperature of 25 °C, low detection limit of 1 ppm (lower than the 1.8 ppm diabetes diagnosis threshold), and high selectivity towards acetone in a mixed gas of acetone and water vapor, hopefully showing promise for application in the much faster and earlier diagnosis of diabetes. V4C3T x MXene is used for the first time in the field of acetone detection in this work, hopefully opening up a path for the investigation of applications of MXene in gas sensors, and such exciting findings distinguish V4C3T x as a comparable material to the well-known Ti3C2T x . In addition, we used DFT calculations to explore the mechanisms that result in the superior selectivity for acetone with respect to water vapor. Hopefully, the proposed mechanisms combining experimental results and theoretical study will shed light on the design and production of new high-performance acetone sensors.

Searching for new TiO2 crystal phases with better photoactivity.

Using the recently developed stochastic surface walking global optimization method, this work explores the potential energy surface of TiO2 crystals aiming to search for likely phases with higher photocatalytic activity. Five new phases of TiO2 are identified and the lowest energy phase transition pathways connecting to the most abundant phases (rutile and anatase) are determined. Theory shows that a high-pressure phase, α-PbO2-like form (TiO2II) acts as the key intermediate in between rutile and anatase. The phase transition of anatase to rutile belongs to the diffusionless Martensitic phase transition, occurring through a set of habit planes, rutile(101)//TiO2II(001), and TiO2II(100)//anatase(112). With regard to the photocatalytic activity, three pure phases (#110, pyrite and fluorite) are found to possess the band gap narrower than rutile, but they are unstable at the low-pressure condition. Instead, a mixed anatase-TiO2II phase is found to have good stability and narrower band gap than both parent phases. Because of the phase separation, the mixed phase is also expected to improve the photocatalytic performance by reducing the probability of the electron-hole pair recombination.

Three-phase junction for modulating electron-hole migration in anatase-rutile photocatalysts.

The heterophase solid-solid junction as an important type of structure unit has wide applications for its special mechanics and electronic properties. Here we present a first three-phase atomic model for the anatase-rutile TiO2 heterophase junction and determine its optical and electronic properties, which leads to resolution of the long-standing puzzles on the enhanced photocatalytic activity of anatase-rutile photocatalysts. By using a set of novel theoretical methods, including crystal phase transition pathway sampling, interfacial strain analysis and first principles thermodynamics evaluation of holes and electrons, we identify an unusual structurally ordered three-phase junction, a layer-by-layer "T-shaped" anatase/TiO2-II/rutile junction, for linking anatase with rutile. The intermediate TiO2-II phase, although predicted to be only a few atomic layers thick in contact with anatase, is critical to alleviate the interfacial strain and to modulate photoactivity. We demonstrate that the three-phase junction acts as a single-way valve allowing the photogenerated hole transfer from anatase to rutile but frustrating the photoelectron flow in the opposite direction, which otherwise cannot be achieved by an anatase-rutile direct junction. This new model clarifies the roles of anatase, rutile and the phase junction in achieving high photoactivity synergistically and provides the theoretical basis for the design of better photocatalysts by exploiting multi-phase junctions.

Serum copper and zinc levels in individuals with autism spectrum disorders.

Trace elements play a critical role in the pathogenesis of autism spectrum disorders (ASD). The aim of this study was to investigate the serum levels of zinc (Zn) and copper (Cu) in Chinese children with ASD. Sixty patients (48 males, 12 females) diagnosed with ASD and 60 healthy sex-matched and age-matched control participants were assessed for serum Zn and Cu content at admission. The severity of ASD was also evaluated using the Childhood Autism Rating Scale (CARS) score. The results indicated that the mean serum Zn levels and Zn/Cu ratio were significantly lower in children with ASD compared with normal cases (P<0.001, respectively), whereas serum Cu levels were significantly higher (P<0.001). There was a significant negative association between Zn/Cu and CARS scores (r=-0.345, P=0.007). On the basis of the receiver operating characteristic curve, the optimal cut-off value of serum levels of Zn/Cu as an indicator for an auxiliary diagnosis of autism was projected to be 0.665, which yielded a sensitivity of 90.0% and a specificity of 91.7%; the area under the curve was 0.968 (95% confidence interval, 0.943-0.993). In conclusion, these results suggested an association between serum levels of Zn and Cu and ASD among Chinese patients, and the Zn/Cu ratio could be considered a biomarker of ASD.

[Study on excess sludge solubilization in S-TE process under microaeration].

The effect of S-TE (solubilization by thermophilic enzyme) pretreatment on excess sludge solubilization and changes of chemical components under microaeration and different temperatures was investigated. The results showed that, two reaction mechanisms of enzyme-catalyzed reaction and thermal-hydrolyzed reaction were involved in the S-TE process, which began with depolymerization of sludge flocs by exoenzymes including proteases and amylases, followed by cell-walls and organic matters disintegration and hydrolyzation. The solubiozation process with thermophilic bacteria Bacillus stearothermophilus sp. AT06-1 addition was enhanced compared with the control (the process without the bacteria). Under the optimum temperature (65 degrees C), the solubilization rate of total suspended solid (TSS) and volatile suspended solid (VSS) reached 34.09% and 24.16% within 2 days respectively, 7.57% and 6.87% higher than the control. The results also revealed that under microaeration operation, the maximal soluble chemical oxygen demand (SCOD) of 4,531 mg/L and volatile fatty acid (VFA) of 2,319 mg/L were obtained, which would be beneficial to the followed anaerobic digestion process. At the same time the activity of protease was dramatically promoted. The protein released from the sludge was hydrolyzed, resulting in an increase of protein concentration at the early stage of the experiment and then a decrease at the later period.