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Carbon quantum dots implanted CdS nanosheets: Efficient visible-light-driven photocatalytic reduction of Cr(VI) under saline conditions
摘要： Chromium(VI) (Cr(VI)), a toxic metal, is generally present together with ionic salts in industrial effluents. An efficient reduction of Cr(VI) to Cr(III) in saline water is an imperative issue but still a challenging task. Literature has rarely addressed reducing Cr(VI) effectively under saline conditions. Herein, carbon quantum dots (CQDs) were successfully implanted in the CdS nanosheets (CdS-NSs) to prepare nanocomposites (i.e., CCNs) for the first time to efficiently reduce Cr(VI) to Cr(III). The newly fabricated CCNs demonstrated superior performance to reduce Cr(VI) compared to pristine CdS-NSs and CQDs-deposited CdS nanosheets (i.e., CQD/CdS-NSs) in saline water. The nanostructures were examined by spectral and photoelectrochemical measurements as well as density functional theory (DFT) calculations. Results showed that CCNs facilitated the photo-electron transport and thus suppressed charge recombination via formation of micro-regional heterostructures. A lower band gap of CCNs relative to pristine CdS-NSs and CQD/CdS-NSs extended the light absorption spectrum. The optimal photocatalyst, denoted as CCNs-2, exhibited an efficiency of ~94% for photocatalytic Cr(VI) reduction within 10 min in water containing 1200 mg/L salts. The obtained rate constant of reduction of Cr(VI) was (2.62 ± 0.04) × 10-1 min-1, approximately 4 and 3 times higher than that of pristine CdS-NSs and CQD/CdS-NSs, respectively. After 3 cycles, the CCNs-2 still showed an efficiency of ~78% aqueous Cr(VI) reduction within 10 min. Our results clearly presented that implantation relative to deposition of CQDs for CdS-NSs is a preferential strategy to enhance photocatalytic Cr(VI) reduction in saline water under visible light irradiation.
关键词： Saline water,Implantation,Photocatalytic Cr(VI) reduction,Carbon quantum dots,Cadmium sulfide nanosheets
更新于2025-09-19 17:13:59
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Classification of saline water for irrigated agriculture using near infrared spectroscopy coupled with pattern recognition techniques
摘要： This research aimed to create near infrared (NIR) spectroscopy models for the classification of saline water with a pattern recognition technique. A total of 112 water samples were collected from the Tha Chin river basin in Thailand. Water samples with salinity less than 0.2 g/l were identified as suitable for agriculture, while water samples with salinity higher than 0.2 g/l were found to be unsuitable. The NIR spectra of water samples were recorded using a Fourier transform (FT) NIR spectrometer in the wavenumber of 12,500–4,000 cm-1. The salinity of each water sample was analysed by electrical conductivity meter. Identification models were established with 5 supervised pattern recognition techniques including k-nearest neighbour (k-NN), support vector machine (SVM), artificial neural network (ANN), soft independent modelling of class analogies (SIMCA), and partial least squares-discriminant analysis (PLS-DA). The performance of the NIR model was carried out with a split-test method. About 80% of spectra (90 spectra) were randomly selected to develop the classification models. After model development, the NIR spectroscopy models were used to classify the categories of the remaining samples (22 samples). The ANN model showed the highest performance for classifying saline water with precision, recall, F-measure and accuracy of 84.6%, 100.0%, 91.7% and 90.9%, respectively. Other techniques presented satisfactory classification results with accuracy greater than 68.2%. This point indicated that NIR spectroscopy coupled with the pattern recognition technique could be applied to classify saline water for agricultural use according to salinity level in natural resources.
关键词： pattern recognition,near infrared spectroscopy,agriculture,saline water
更新于2025-09-11 14:15:04
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Characterization of CDOM in saline and freshwater lakes across China using spectroscopic analysis
摘要： Colored dissolved organic matter (CDOM) is a major component of DOM in waters, and plays a vital role in carbon cycling in inland waters. In this study, the light absorption and three-dimensional excitation-emission matrix spectra (EEMs) of CDOM of 936 water samples collected in 2014–2017 from 234 lakes in five regions across China were examined to determine relationships between lake water sources (fresh versus saline) and their fluorescence/absorption characteristics. Results indicated significant differences regarding DOC concentration and aCDOM(254) between freshwater (6.68 mg C L-1, 19.55 m-1 ) and saline lakes (27.4 mg C L-1, 41.17 m-1). While humic-like (F5) and fulvic-like (F3) compounds contributed to CDOM fluorescence in all lake waters significantly, their contribution to total fluorescence intensity (FT) differed between saline and freshwater lakes. Significant negative relationships were also observed between lake altitude with either F5 (R2=0.63, N=306) or FT (R2=0.64, N=306), suggesting that the abundance of humic-like materials in CDOM tends to decrease with increased in lakes altitude. In high-altitude lakes, strong solar irradiance and UV exposure may have induced photo-oxidation reactions resulting in decreased abundance of humic-like substances and the formation of low molecular weight compounds. These findings have important implications regarding our understanding of C dynamics in lacustrine systems and the contribution of these ecosystems to the global C cycle.
关键词： CDOM,EEMs,Absorption,saline water,freshwater
更新于2025-09-04 15:30:14