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The catalytic transformation of CO 2 into valuable products has garnered wide interest owing to both economic and environmental benefits, in which the chemical fixation of CO 2 into carbonate structures represents a crucial step that occurs on the adsorbed catalyst surfaces. Transition metal oxides with acidic and basic active sites have exhibited potential in promoting the carbonation of weakly bound CO 2 molecules. Here, the interactions between CO 2 molecules and the Sc 3 O 4 + cation in the gas phase are investigated by using infrared photodissociation spectroscopy in conjunction with quantum chemical calculations. Both end-on and various carbonate-containing configurations, including center and bridge carbonate structures, have been theoretically identified for the CO 2 -coordinated ion-molecule complexes. Based on the comparison between the experimental spectra and simulated spectra of low-lying isomers in the CO 2 antisymmetric stretching vibrational frequency region, isomers characterized by a bridge carbonate core structure are demonstrated to be the major contributors to the observed spectra. Examination of potential energy surfaces reveals lower energy barriers and simpler reaction routes for the conversion of molecularly bound CO 2 into a bridge carbonate moiety, providing reasonable explanations for their prevalence in the experiments.

Carbon dioxide (CO 2 ) adsorption is a critical step to curbing carbon emissions from fossil fuel combustion. Among various options, transition metal oxides have received extensive attention as promising CO 2 adsorbents due to their affordability and sustainability for large-scale use. Here, the nature of binding interactions between CO 2 molecules and cationic scandium oxides of different sizes, i.e., ScO + , Sc 2 O 2 + , and Sc 3 O 4 + , is investigated by mass-selective infrared photodissociation spectroscopy combined with quantum chemical calculations. The well-accepted electrostatic considerations failed to provide explanations for the trend in the binding strengths and variations in the binding orientations between CO 2 and metal sites of cationic scandium oxides. The importance of orbital interactions in the driving forces for CO 2 adsorption on cationic scandium oxides was revealed by energy decomposition analyses. A molecular surface property, known as the local electron attachment energy, is introduced to elucidate the binding affinity and orientation-specific reactivity of cationic scandium oxides upon the CO 2 attachment. This study not only reveals the governing factor in the binding behaviors of CO 2 adsorption on cationic scandium oxides but also serves as an archetype for predicting and rationalizing favorable binding sites and orientations in extended surface-adsorbate systems.

The signal of the traditional chromogenic systems is directly proportional to analyte concentration, leading to an unsatisfactory sensitivity. Herein, we report a cascade chromogenic system to realize exponential amplification of colorimetric signal through coupling chemical oxidation with photoinduced radical chain reaction. The chemical oxidation of o -phenylenediamine (OPD) by Fe 3+ generates Fe 2+ and photoactive 2,3-diaminophenazine (DAP). Under blue-light irradiation, DAP initiates the formation of holes and H 2 O 2 that reacts with Fe 2+ to hydroxyl radicals (·OH) and Fe 3+ via an intersystem crossing (ISC) process. Moreover, the holes oxidize water to yield ·OH as well. The resulting ·OH and regenerated Fe 3+ in turn oxidize OPD to yield more DAP, leading to a self-propagating reaction cycle that continues to proceed until all the OPD molecules are consumed, along with a distinct color change from colorless to yellow. Through the generation of the complex between DAP and acetone that limits the ISC process, and therefore quenches the colorimetric signal, the highly sensitive and selective naked-eye detection of acetone is achieved from 50 μM to 3 mM, with a limit of detection of 35 μM. Additionally, the feasibility of this colorimetric assay to detect acetone in real water samples is also demonstrated.

We report a visual chronometric assay for Cr 3+ based on the Cu 2 O nanocube-mediated clock reaction of methylene blue (MB) and N 2 H 4 . MB with a blue color can be easily reduced by excess N 2 H 4 to form colorless leuco-MB in the presence of Cu 2 O nanocubes as a catalyst in a short time. However, the addition of Cr 3+ decreases the catalytic activity of Cu 2 O nanocubes owing to the coordination interactions between them, leading to an increase in the reaction time. The reaction time change was employed for selective detection of Cr 3+ . This assay has a wide dynamic range from 0.03 to 600 μM with a limit of detection of 2.7 nM. Remarkably, different concentrations of Cr 3+ can be directly detected with the naked eye by observing the color-fading speed. Additionally, this assay was successfully used to determine Cr 3+ in real water samples.

A chemiluminescence (CL) sensing method for amino acid discrimination based on luminol functionalized silver nanoparticles (LumAgNPs) has been developed. Luminescence emission in the presence of hydrogen peroxide under neutral conditions was characterized in three ways: the time required for the signal to appear (Ta), the time required to reach maximum luminescence (Tp), and CL intensity. These factors were found to change upon interaction of the nanoparticles with various amino acids, leading to distinct response patterns characteristic of each analyte. Seven amino acids (l-cysteine, l-proline, l-phenylalanine, l-arginine, l-threonine, l-glutamic acid, and l-tyrosine) were identified at a concentration of 10 ng/mL. This sensitivity is about 3 orders of magnitude better than that of recently reported methods based on fluorescent sensor arrays using cucurbit[n]uril and comparable to high-performance liquid chromatography. Application to 27 unknown samples gave a 96.3% success rate at the 10 ng/mL level.

In this work, we developed a simple, facile, and highly sensitive nanoparticle-based chemiluminescent (CL) sensor array for the discrimination of organophosphate and carbamate pesticides. This CL sensor array is based on simultaneous utilization of the triple-channel properties of the luminol-functionalized silver nanoparticle (Lum-AgNP) and H2O2 CL system containing CL intensity, the time for CL emissions to appear, and the time to reach the CL peak value, which are able to be measured via a single experiment. The triple-channel properties can be simultaneously altered after interaction with pesticides, producing distinct CL response patterns as "fingerprints" related to each specific pesticide, which was subjected to principal component analysis (PCA) to generate a clustering map. Using this sensor array, five organophosphate and carbamate pesticides, including dimethoate, dipterex, carbaryl, chlorpyrifos, and carbofuran, have been well-distinguished at a concentration of 24 μg/mL. A total of 20 unknown pesticide samples have been successfully identified with an accuracy of 95%. The simple strategy of this study is expected to promote the development of functionalized nanomaterial-based sensor arrays.