Locust powder was converted into water-soluble fluorescent nitrogen-doped carbon dots (N-CDs) with gram-scale yield through a self-exothermic reaction between nitric acid and diethylenetriamine (DETA) within 10 min. The morphology, elemental information, and optical properties of the N-CDs were characterized using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Fouriertransform infrared, ultraviolet-visible and fluorescence spectroscopy. Spectroscopic investigation indicated that the fluorescence emission behaviour of N-CDs is excitation wavelength dependent, with the strongest emission peak at 470 nm using a 390 nm excitation wavelength. The strong absorption peak of sunset yellow (SY) at 482 nm overlaps substantially with the blue emission peak (470 nm) of N-CDs. This
We investigated the effect of soluble Ca on the speciation of Pb in phosphate-amended soils. A calcareous soil was amended in sequence with soluble phosphate (0 and 299 mg kg P), calcium nitrate (0, 200, and 400 mg kg Ca), and/or lead nitrate (0 and 1000 mg kg Pb) and incubated for 50 d. Extractable Ca was relatively similar across all samples, with a minor reduction in Ca release for treatments amended with P possibly from the formation of Ca-phosphate minerals. Olsen-P extractability from P-added treatments was highest in the non-Pb-amended soils and was about 40% lower when Pb was added as a result of Pb-phosphate formation. In the absence of P, diethylene triamine pentaacetic acid (DTPA)-Pb extractability increased with increasing Ca amendment; however, in the P-amended treatments, DTPA-Pb decreased with increasing Ca addition. X-ray absorption spectroscopy results of the Pb spiked soils indicate that adsorbed Pb is the primary phase (up to 92%) in non-P-amended soils with minor distribution to hydrocerussite and Pb-phosphate phases. In the P-amended treatments, Pb speciation shifted to Pb-phosphate [chloropyromorphite and Pb(PO)] (42-48%) and adsorbed Pb (44-50%). As Ca concentration increased in the P-amended soils, Pb-phosphate speciation moved from combined chloropyromorphite and Pb(PO) (0 mg kg Ca) to exclusively chloropyromorphite. The study demonstrates that soluble Ca enhances Pb immobilization with P amendments.
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