Probing the crystal structure, composition-dependent absolute energy levels, and electrocatalytic properties of silver indium sulfide nanostructures

The absolute electronic energy levels in silver indium sulfide (AIS) nanocrystals (NCs) with varying compositions and crystallographic phases have been determined by using cyclic voltammetry. Different crystallographic phases, that is, metastable cubic, orthorhombic, monoclinic, and a mixture of cubic and orthorhombic AIS NCs, were studied. The band gap values estimated from the cyclic voltammetry measurements match well with the band gap values calculated from the diffuse reflectance spectra measurements. The AIS nanostructures were found to show good electrocatalytic activity towards the hydrogen evolution reaction (HER). Our results clearly establish that the electronic and electrocatalytic properties of AIS NCs are strongly sensitive to the composition and crystal structure of AIS NCs. Monoclinic AIS was found to be the most active HER electrocatalyst, with electrocatalytic activity that is almost comparable to the MoS_2^-based nanostructures reported in the literature, whereas cubic AIS was observed to be the least active of the studied crystallographic phases and compositions. In view of the HER activity and electronic band structure parameters observed herein, we hypothesize that the Fermi energy level of AIS NCs is an important factor that decides the electrocatalytic efficiency of these nanocomposites. The work presented herein, in addition to being the first of its kind regarding the composition and phase-dependence of electrochemical aspects of AIS NCs, also presents a simple solvothermal method for the synthesis of different crystallographic phases with various Ag/In molar ratios

In Situ Detection of the Adsorbed Fe(II) Intermediate and the Mechanism of Magnetite Electrodeposition by Scanning Electrochemical Microscopy

Electrodeposition is an important approach that can produce functional compound materials by assembling multiple species at the electrode surface. However, a fundamental understanding of the electrodeposition mechanism has been limited by its complexity and is often gained only through ex situ studies of deposited materials. Here we report on the application of scanning electrochemical microscopy (SECM) to enable the in situ, real-time, and quantitative study of electrodeposition and electrodissolution. Specifically, we electrodeposit magnetite (Fe₃O₄) from an alkaline solution of Fe­(III)–triethanolamine as a robust route that can prepare this magnetic and electrocatalytic compound on various conductive substrates. The powerful combination of SECM with cyclic voltammetry (CV) at a gold substrate reveals that the electrodeposition of magnetite requires the preceding adsorption of Fe­(II)–triethanolamine on the substrate surface and, subsequently, is mediated through the highly complicated EC_adsC_mag mechanism, where both chemical steps occur at the substrate surface rather than in the homogeneous solution. SECM-based CV is obtained under high mass-transport conditions and analyzed by the finite element method to kinetically resolve all steps of the EC_adsC_mag mechanism and quantitatively determine relevant reaction parameters. By contrast, the adsorbed Fe­(II) intermediate is unresolvable from co-deposited magnetite in situ by other electrochemical techniques and is undetectable ex situ because of the facile air oxidation of the Fe­(II) intermediate. Significantly, SECM-based CV will be useful for the in situ characterization of various electrodeposited compounds to complement their ex situ characterization

Management and Outcomes Following Surgery for Gastrointestinal Typhoid: An International, Prospective, Multicentre Cohort Study

Background: Gastrointestinal perforation is the most serious complication of typhoid fever, with a high disease burden in low-income countries. Reliable, prospective, contemporary surgical outcome data are scarce in these settings. This study aimed to investigate surgical outcomes following surgery for intestinal typhoid. Methods: Two multicentre, international prospective cohort studies of consecutive patients undergoing surgery for gastrointestinal typhoid perforation were conducted. Outcomes were measured at 30 days and included mortality, surgical site infection, organ space infection and reintervention rate. Multilevel logistic regression models were used to adjust for clinically plausible explanatory variables. Effect estimates are expressed as odds ratios (ORs) alongside their corresponding 95% confidence intervals. Results: A total of 88 patients across the GlobalSurg 1 and GlobalSurg 2 studies were included, from 11 countries. Children comprised 38.6% (34/88) of included patients. Most patients (87/88) had intestinal perforation. The 30-day mortality rate was 9.1% (8/88), which was higher in children (14.7 vs. 5.6%). Surgical site infection was common, at 67.0% (59/88). Organ site infection was common, with 10.2% of patients affected. An ASA grade of III and above was a strong predictor of 30-day post-operative mortality, at the univariable level and following adjustment for explanatory variables (OR 15.82, 95% CI 1.53–163.57, p = 0.021). Conclusions: With high mortality and complication rates, outcomes from surgery for intestinal typhoid remain poor. Future studies in this area should focus on sustainable interventions which can reduce perioperative morbidity. At a policy level, improving these outcomes will require both surgical and public health system advances