Effect of Heat Treatment on the Microstructure and Mechanical Properties of the Al0.6CoCrFeNi High-Entropy Alloy.

The effect of heat treatment on the microstructure and tensile properties of an as-cast Al0.6CoCrFeNi high-entropy alloy (HEA) was investigated in this paper. The results show that the as-cast Al0.6CoCrFeNi HEA presents a typical FCC dendrite morphology with the interdendritic region consisting of BCC/B2 structure and heat treatment can strongly affect the microstructure and mechanical properties of HEA. Microstructure analysis revealed the precipitation of a nano-sized L12 phase in the FCC dendrite and the formation of the FCC and σ phases in the interdendritic region after annealing at 700 °C. The coarse B2 phase was directly precipitated from the FCC dendrite in the 900 °C-annealed sample, with the coexistence of the B2, FCC, and σ phases in the interdendritic region. Then, the interdendritic region converted to a B2 and FCC dual-phase structure caused by the re-decomposition of the σ phase after annealing at 1100 °C. The tensile test results show that the 700 °C-annealed HEA presents the most significant strengthening effect, with increments of corresponding yield strength being about 107%, which can be attributed to the numerous nano-sized L12 precipitates in the FCC dendrite. The mechanical properties of 1100 °C-annealed alloy revert to a level close to that of the as-cast alloy, which can be attributed to the coarsening mechanism of B2 precipitates and the formation of a soft FCC phase in the interdendritic region. The observed variation in mechanical properties during heat treatment follows the traditional trade-off relationship between strength and plasticity.

L-Cysteine functionalized graphene oxide nanoarchitectonics: A metal-free Hg2+ nanosensor with peroxidase-like activity boosted by competitive adsorption.

Developing non-noble metal, even metal-free chemical sensors for the detection of toxic heavy metal ions is significantly desirable for economically and environmentally sustainable application but has heretofore remained elusive. Herein, a L-cysteine functionalized graphene oxide nanosheet (CGO) nanoarchitectonics, greenly synthesized by a very simple method at room temperature, was utilized to realize the simultaneous enrichment and colorimetric detection of trace mercury ions (Hg2+). It was discovered that CGO, as a nanozyme mimic exhibited greatly enhanced peroxidase-like catalytic activity than the pristine graphene oxide. By exploring the interactions of CGO nanozyme with colorimetric substrate, 3,3',5,5'-tetramethylbenzidine (TMB) and target Hg2+ ions, we found that the sensing principle was based mainly on the competitive adsorption between Hg2+ ions and TMB over CGO. The pre-capture of Hg2+ ions hindered the TMB binding on CGO, resulting in the promoted oxidation of TMB by H2O2 to produce more colored oxidation products, from which the colorimetric sensing of Hg2+ was realized with a good detection effect on 5 µg L-1 solution. As an enrichment-sensing integration platform, this metal-free sensor is cost-effective and sensitive, and presents considerable anti-interference ability over other metal ions. Overall, this work not only expands the application of graphene-based materials in colorimetric detection but also provides a general sensing principle to construct highly sensitive sensors.

Portable Hg2+ Nanosensor with ppt Level Sensitivity Using Nanozyme as the Recognition Unit, Enrichment Carrier, and Signal Amplifier.

We report a portable and highly sensitive Hg2+ nanosensor, where the CuS nanozyme functions as an Hg2+ recognition unit, a Hg2+ enrichment/preconcentration carrier, and a signal amplifier/output unit. The as-designed enrichment-detection integration strategy is customizable and endows the sensor with both a wide detection range from 50 ppt to 400 ppb and a high sensitivity with a minimum detectable Hg2+ concentration of 50 ppt. In order to make the Hg2+ nanosensor portable and cost-effective, a commercial RGB sensor is employed here in conjunction with the Hg2+-dependent colorimetric reaction. More importantly, the as-developed Hg2+ nanosensor is feasible for analysis of real samples with satisfactory accuracy (deviation <10%) and reproducibility (recovery ∼82%). Thus, this portable Hg2+ nanosensor appears to be a viable solution to meet the actual needs of on-site and real-time mercury contamination analysis and may also pave the way to colorimetric nanosensors for other metal ions.