Simultaneous Detection of CO and NH3 Gases at Room Temperature with an Array of ZnS Chemiresistive Sensors and the Superposition Principle

Simultaneous detection of multiple toxic gases in the air using room temperature gas sensors is significant in low-power environmental monitoring applications. However, the low-temperature resistive gas sensors are sensitive to more than one gas, and thus, an array of gas sensors and high energy-consuming machine learning algorithms are required to predict the concentrations of the individual gases in mixed target gas. Here, we report a computationally less intensive method to predict the composition of the target gases using linear gas sensors. A sensor array consisting of two ZnS resistive gas sensors biased at different voltages in conjunction with the superposition principle is used to predict the concentration of individual gases in the binary mixture of NH₃ and CO present in the air. Further, the effect of humidity on response is mitigated by formulating the sensitivity of the sensors as a function of relative humidity. The proposed algorithm predicted the concentration of the individual gases in mixed gas with a maximum absolute error of ∼15% irrespective of humidity levels, which is practically allowed in most gas sensing applications. As the superposition principle is a low-power consuming technique, the proposed approach can be used in applications where trace levels of gases in mixed targets need to be detected with energy-efficient methods.

Ethylenediamine-assisted growth of multi-dimensional ZnS nanostructures and study of its charge transfer mechanism on supercapacitor electrode and photocatalytic performance

In recent years, much interest has been raised by materials with multi-purpose characteristics as the performance of electrochemical energy devices such as supercapacitors and photocatalytic activities depend strongly on the properties of materials. This study delineates various parameters like morphology, energy band gap, charge transfer resistance, different defect states, diffusion coefficient and functional groups adsorbed on the surface of material to assess the performance of supercapacitor electrodes and photocatalytic degradation efficiency of synthesised multi-dimensional ZnS nanostructures. Ethylenediamine (EN)-mediated multi-dimensional ZnS nanostructures were grown by the solvothermal route. One-dimensional (1D), 2D and 3D morphologies were obtained by varying the ratio of de-ionised water and EN, taken as 1:3, 1:2 and 1:1, respectively. The EN molecules effectively capped most of the surfaces of the ZnS nanoparticles formed, preventing agglomeration of nanoparticles due to the decrement in surface energy. The oriented attachment of these clusters resulted in the formation of 1D, 2D and 3D morphologies. The plausible chemistry in the formation of 1D, 2D and 3D nanostructures has been elaborated. Charge transfer properties of prepared electrodes have been examined using the electrochemical impedance spectroscopy (EIS) technique because better charge transfer causes diminishing electron/hole recombination and hence better photodegradation efficiency. Among the synthesised materials, the 2D nanostructure degraded the eosin Y dye to maximum 90.71% efficiency with rate constant 34 × 10^-3 min^-1. 2D nanostructures possess better charge transfer and hence better photodegradation efficiency. Various studies using methods of UV-vis, Fourier-transform infrared, Brunauer-Emmett-Teller, x-ray photoelectron spectroscopy and photoluminescence spectra are in good agreement with the obtained photodegradation results. After analysing cyclic voltammetry curves and EIS, a higher diffusion coefficient is obtained for 1D nanostructure material, hence a higher specific capacitance and higher energy density of 159.12 F g^-1 and 22.75 KWh kg^-1 are found in this case. Only 9% loss of specific capacitance is found after 1000 cycles, showing a relatively high cycling stability in 3D nanostructures. The excellent supercapacitive property can be attributed to the porous structure and high specific surface area. Thus, the synthesised multi-dimensional ZnS nanostructures are proved to be a potential candidate for both photocatalytic and supercapacitor electrode performance.

Primitive Photosynthetic Architectures Based on Self-Organization and Chemical Evolution of Amino Acids and Metal Ions

The emergence of light-energy-utilizing metabolism is likely to be a critical milestone in prebiotic chemistry and the origin of life. However, how the primitive pigment is spontaneously generated still remains unknown. Herein, a primitive pigment model based on adaptive self-organization of amino acids (Cystine, Cys) and metal ions (zinc ion, Zn2+) followed by chemical evolution under hydrothermal conditions is developed. The resulting hybrid microspheres are composed of radially aligned cystine/zinc (Cys/Zn) assembly decorated with carbonate-doped zinc sulfide (C-ZnS) nanocrystals. The part of C-ZnS can work as a light-harvesting antenna to capture ultraviolet and visible light, and use it in various photochemical reactions, including hydrogen (H2) evolution, carbon dioxide (CO2) photoreduction, and reduction of nicotinamide adenine dinucleotide (NAD+) to nicotinamide adenine dinucleotide hydride (NADH). Additionally, guest molecules (e.g., glutamate dehydrogenase, GDH) can be encapsulated within the hierarchical Cys/Zn framework, which facilitates sustainable photoenzymatic synthesis of glutamate. This study helps deepen insight into the emergent functionality (conversion of light energy) and complexity (hierarchical architecture) from interaction and reaction of prebiotic molecules. The primitive pigment model is also promising to work as an artificial photosynthetic microreactor.

Synthesis, Characterisation, and Photocatalytic Behaviour of Mesoporous ZnS Nanoparticles Prepared Using By-Product Templating

High surface area mesoporous ZnS nanoparticles (MZN) were obtained with the aid of the by-product of the synthesising reaction. This by-product, namely NaNO3, can be considered as a soft template responsible for the formation of pores. Ethanol and water were chosen as the synthesis media. Ultrasonic waves were used as an accelerator for the synthesis of MZNs. Photocatalytic activities of the synthesised samples for the degradation of methylene blue (MB) were investigated under ultraviolet irradiation. Synthesised specimens were characterised using field emission scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, diffuse reflectance spectroscopy, N2-physisorption, and FT-IR spectroscopy. Results indicated that the synthesis media has a pronounced effect on the surface properties of the final porous particles by several mechanisms. The specific surface area of the MZN samples synthesised in water and ethanol were determined to be 53 and 201 m2 g−1, respectively. The difference in the specific surface area was attributed to the weak solvation of S2− ions (Na2S·5H2O in ethanol) and also to the by-product of the synthesis reaction. The photocatalytic behaviour of the mesoporous ZnS nanoparticles synthesised in these two media were investigated and the results have been interpreted with the aid of effective surface area, pore volume, and bandgap energy of the specimens.

Visible-Light-Assisted Photocatalytic Reduction of Nitroaromatics by Recyclable Ni(II)-Porphyrin Metal-Organic Framework (MOF) at RT

A microporous Ni(II)-porphyrin metal-organic framework (MOF), [Ni3(Ni-HTCPP)2(μ2-H2O)2(H2O)4(DMF)2]·2DMF, (MOF1) (where, Ni-HTCPP = 5,10,15,20-tetrakis(4-benzoate) porphyrinato-Ni(II)) has been synthesized by the solvothermal route. Single-crystal X-ray diffraction study of 1 reveals a 2D network structure constituted by Ni3 cluster and [Ni-HTCPP](3-) metalloligand having (3, 6)-connected binodal net with {4(3)}2{4(6)·6(6)·8(3)}-kgd net topology. The 2D layers are further stacked together through π-π interactions between the porphyrin linkers to generate a 3D supramolecular framework which houses 1D channels with dimension of ∼5.0 × 9.0 Å(2) running along the crystallographic a-axis. Visible-light-assisted photocatalytic investigation of MOF1 for heterogeneous reduction of various nitroaromatics at room temperature resulted in the corresponding amines with high yield and selectivity. On the contrary, the Ni(II)-centered porphyrin tetracarboxylic acid [Ni-H4TCPP] metalloligand does not show the photocatalytic activity under similar conditions. The remarkably high catalytic performance of MOF1 over [Ni-H4TCPP] metalloligand has been attributed due to cooperative catalysis involving the Ni-centered porphyrin secendary building units (SBUs) and the Ni3-oxo node. Further, the MOF1 was recycled and reused up to three cycles without any significant loss of catalytic activity as well as structural rigidity. To the best of our knowledge, MOF1 represents the first example of MOF based on 3d metal ion exhibiting visible-light-assisted reduction of nitroaromatics under mild conditions without the assistance of noble metal cocatalysts.

Green synthesis, optical and magnetic properties of a MnIImetal–organic framework (MOF) that exhibits high heat of H2adsorption

Green synthesis of a 3D, Mn(ii) MOF, [Mn₃(NDC)₃(DMA)₄]n(1) has been achieved by employing mechanochemical and sonochemical routes and1′exhibits an interesting gas uptake properties with a high value of isosteric heat of adsorption (Q_st) for H₂.

Template-free syntheses of hierarchical PbS microstructures using a new sulphur source and their time-dependent morphological evolution and photocatalytic properties

Template-free PbS microstructures composed of nanocrystals exhibiting time-dependent morphological evolution from cubes to dendrites were synthesised by one-pot solvothermal route using DBDS as a new temperature controlled in situ source of S²⁻ ions.