Ratiometric fluorescence detection of Cu2+ based on carbon dots/bovine serum albumin-Au nanoclusters.

A ratiometric fluorescence sensor for Cu2+ detection was developed by employing carbon dots (CDs) as the reference fluorophore, and bovine serum albumin (BSA)-Au nanoclusters (AuNCs) both as specific recognition element and as response signal. The CDs were prepared by heating an acetic acid solution of chitosan at 180°C. The proposed nanoprobe was prepared by simply mixing the CDs and BSA-AuNCs. Here, the CDs were associated with BSA-AuNCs to form CDs/BSA-AuNCs nanoprobes based on electrostatic interaction and hydrogen bonds. In the hybrid fluorescent CDs/BSA-AuNCs nanoprobe, the emission of BSA-AuNCs at 640 nm was quenched by Cu2+, whereas the emission of CDs at 424 nm was maintained. The fluorescence changes of I640/I424 had good linearity with Cu2+ concentration in the range 1.5-600 nM, and the detection limit of the nanoprobe was 0.5 nM for Cu2+ detection, almost 4 × 104 times lower than the maximum allowable amount of Cu2+ in drinking water. The proposed method for detecting Cu2+ also had high selectivity and feasibility.

Ratiometric fluorescence detection of superoxide anion based on AuNPs-BSA@Tb/GMP nanoscale coordination polymers.

A novel ratiometric fluorescence nanosensor for superoxide anion (O2•- ) detection was designed with gold nanoparticles-bovine serum albumin (AuNPs-BSA)@terbium/guanosine monophosphate disodium (Tb/GMP) nanoscale coordination polymers (NCPs) (AuNPs-BSA@Tb/GMP NCPs). The abundant hydroxyl and amino groups of AuNPs-BSA acted as binding points for the self-assembly of Tb3+ and GMP to form core-shell AuNPs-BSA@Tb/GMP NCP nanosensors. The obtained probe exhibited the characteristic fluorescence emission of both AuNPs-BSA and Tb/GMP NCPs. The AuNPs-BSA not only acted as a template to accelerate the growth of Tb/GMP NCPs, but also could be used as the reference fluorescence for the detection of O2•- . The resulting AuNPs-BSA@Tb/GMP NCP ratiometric fluorescence nanosensor for the detection of O2•- demonstrated high sensitivity and selectivity with a wide linear response range (14 nM-10 µM) and a low detection limit (4.7 nM).

Release of fluorine and chlorine during increase of phosphate rock grade by calcination and digestion.

A series of experiments for calcination and subsequent digestion to increase the grade of phosphate rock were performed. Fluorine and chlorine released by calcination and digestion were investigated. The forms of both elements were studied by sequential chemical extraction. The grades of raw and calcined phosphate rocks, and their phosphorus concentrates were confirmed according to the value of P2O5%. The results showed that fluorine and chlorine in phosphate rock mainly existed in carbonate-bound and residual forms. The grade of phosphate rock can be well increased by calcination and subsequent digestion. By digestion at the optimal condition of 2.5:1 for liquid-solid ratio, 60 °C for digestion temperature and 50 min for digestion time, the phosphorus concentrates digested from the calcined phosphate rock of 1000 °C reached the highest grade (P2O5% = 33.24%). By calcination, the released fluorine was mainly HF at a low temperature and SiF4 at a high temperature, with fluorine release amount of 1.61 × 104-3.82 × 104 g/t at 900-1100 °C. Cl2, HCl and Cl- were mainly released at 200-500 °C, less than 800 °C and more than 800 °C, which release amount were 9.40 × 10-2.54 × 102 g/t, 2.10 × 102-1.53 × 104 g/t and 2.24 × 102-5.61 × 102 g/t, respectively. By digestion with water for the calcined phosphate rock of 900-1100 °C, the concentrations of fluorine and chlorine in effluent were respectively 77.2-160 mg/L and 7.99-19.6 mg/L. It can be concluded that fluorine and chlorine released by calcination for phosphate rock contribute greatly to atmospheric acid rain and equipment corrosion; by digestion, the discharge of fluorine seriously exceeds the standard and may cause greater pollution to the water body.

Release behavior of iodine during leaching and calcination of phosphate rock.

A series of experiments of column leaching under different pHs (pH 1.8, 3.8, 6.5, and 8.5) and calcination at different temperatures (200-1100 °C) were carried out for evaluation of release behavior of iodine in phosphate rock. The modes of occurrence of iodine in the phosphate rock and its leaching and calcination residues were extracted with sequential chemical extraction. Iodine in solution and solid samples was measured with ion chromatography (IC) and pyrohydrolysis combined ion chromatography (PIC), respectively. Mineralogical compositions of phosphate rock and the leached and calcined residues were determined by XRD (X-ray diffraction) and FT-IR (Fourier infrared spectrum). The results show that iodine in phosphate rock occurred in a descending order of significance, as forms of residual, carbonate bound, ion-exchange, organic bound, Fe-Mn oxide bound, and water soluble. Under pH 1.8, 3.8, 6.5, and 8.5, the release iodine may almost reach the maximum at the leaching time of 65, 93, 90, and 165 h, with leaching rates of 5.28%, 1.24%, 0.550%, and 1.08% and the average iodine concentrations in the leachates of 2300 µg/L, 378 µg/L, 164 µg/L, and 189 µg/L, respectively. The forms of the leached iodine were mostly ion-exchange and carbonate-bound iodine under pH 1.8 and water soluble and ion-exchange iodine under pH 3.8, 6.5, and 8.5. By calcination, the total iodine was released rapidly in 200-300 °C and 700-1000 °C, and almost released completely at 1000 °C, with a leaching rate of 96.6%. The ion-exchange and organic-bound iodine were, respectively, released at 200-1000 °C and at less than 300 °C; the carbonate-bound and residual iodine were mainly released at more than 700 °C. The release iodine in phosphate rock leached by natural water and calcined at a high temperature may lead to the increase of iodine concentration of water body and atmosphere.

Luminescent SiO2@Tb/guanosine 5'-monophosphate core-shell nanoscale coordination polymers for superoxide anion detection.

It is of great significance for superoxide anion (O2•-) detection due to its important role in regulation of biological function. The nanoscale coordination polymers (NCPs) core-shell nanostructures have attracted increasing interests for their nanosized-dependent properties. In this study, SiO2@Tb/guanosine 5'-monophosphate (GMP) NCPs with core-shell nanostructures was designed for O2•- detection. The SiO2@Tb/GMP NCPs core-shell nanostructures were produced by using SiO2 nanoparticles (NPs) as template to control their nano-size. First, Tb3+ was adsorbed on the surface of SiO2NPs by coordination with -COOH of SiO2NPs. Then the Tb/GMP NCPs shells were grown along the surface of SiO2NPs. The SiO2@Tb/GMP NCPs core-shell nanostructures were characterized with scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and Zeta potential. The resulted SiO2@Tb/GMP NCPs core-shell nanostructures displayed strong Tb/GMP emission which decreased linearly with the increased O2•- concentration in the range from 5.3 nM to 6.0 µM with a limit detection of 2.18 nM. And the SiO2@Tb/GMP NCPs core-shell nanostructures also exhibited good selectivity and high sensitivity in HEPES buffer at pH 7.4.

[Study on modes of occurrence of bromine in coals using sequential chemical extraction procedure].

Modes of occurrence of bromine in eight coals from Sichuan and Chongqing were studied using inductively coupled plasma spectrometry and sequential chemical extraction. The results showed that the bromine mainly occur the water-soluble, ion exchangeable, carbonate, Fe-Mn oxides and organic fraction in these coals, which average total extraction rate was 88.2%. In bituminous coal and anthracite, the mean relative amount was 22.3% and 20.0% for organic bromine, 14.0% and 19.2% for the bromine of carbonate bound and almost equal for the bromine from water soluble and Fe-Mn oxidizes. The ion exchangeable bromine may be mainly adsorbed to organic matter in these coals. The relative amount of bromine in various modes of occurrence may not be very closely related to its sedimentary environment during the formation of coal. Bromine in coals from Sichuan and Chongqing should be paid more attention because its potential leachable rate was 36.62% - 86.80% and potential leachable content was 7.092- 20.10 microg/g.