Nonequilibrium Anion Detection in Solid-Contact Ion-Selective Electrodes.

Low-cost and portable nitrate and phosphate sensors are needed to improve farming efficiency and reduce environmental and economic impact arising from the release of these nutrients into waterways. Ion selective electrodes (ISEs) could provide a convenient platform for detecting nitrate and phosphate, but existing ionophore-based nitrate and phosphate selective membrane layers used in ISEs are high cost, and ISEs using these membrane layers suffer from long equilibration time, reference potential drift, and poor selectivity. In this work, we demonstrate that constant current operation overcomes these shortcomings for ionophore-based anion-selective ISEs through a qualitatively different response mechanism arising from differences in ion mobility rather than differences in ion binding thermodynamics. We develop a theoretical treatment of phase boundary potential and ion diffusion that allows for quantitative prediction of electrode response under applied current. We also demonstrate that under pulsed current operation, we can create functional solid-contact ISEs using lower-cost molecularly imprinted polymers (MIPs). MIP-based nitrate sensors provide comparable selectivity against chloride to costlier ionophore-based sensors and exhibit >100,000 times higher selectivity against perchlorate. Likewise, MIP-based solid contact ion-selective electrode phosphate sensors operated under pulsed current provide competitive selectivity against chloride, nitrate, perchlorate, and carbonate anions. The theoretical treatment and conceptual demonstration of pulsed-current ISE operation we report will inform the development of new materials for membrane layers in ISEs based on differences in ion mobility and will allow for improved ISE sensor designs.

Exploring the visible light-assisted conversion of CO2 into methane and methanol, using direct Z-scheme TiO2@g-C3N4 nanosheets: synthesis and photocatalytic performance.

The rapid growth of carbon dioxide (CO2) emissions raises concern about the possible consequences of atmospheric CO2 increase, such as global warming and greenhouse effect. Photocatalytic CO2 conversion has attracted researchers' interests to find a sustainable route for its elimination. In the present study, a direct Z-scheme TiO2/g-C3N4 composite (T-GCN) was fabricated via a facile hydrothermal route for the photocatalytic reduction of CO2 into methane (CH4) and methanol (CH3OH), under visible light irradiation without an electron mediator. The microstructure of the as-obtained TiO2/g-C3N4 nanocomposites was fully characterized for its physicochemical, structural, charge separation, electronic, and photo-excited carrier separation properties. The effect of CO2 and H2O partial pressure was studied to find the best operational conditions for obtaining maximum photocatalytic efficiency; the PCO2 and PH2O were 75.8 and 15.5 kPa, respectively, whereas, by increasing the light intensity from 20 to 80 mW/cm2, a remarkable improvement in the reduction rate takes place (from 11.04 to 32.49 µmol.gcat-1.h-1 methane production, respectively). Finally, under the most favorable light, PCO2 and PH2O conditions, high methanol and methane rates were obtained from the CO2 photocatalytic reduction through T-GCN (1.44 µmol.gcat.-1.h-1 and 32.49 µmol.gcat.-1.h-1, respectively) and an integrated proposition for the Z-scheme mechanism of photocatalytic reduction was proposed. This study offers a promising strategy to synthesize a Z-scheme T-GCN heterojunction with high photocatalytic performance for effective CO2 conversion.

Sono-photocatalytic degradation of tetracycline and pharmaceutical wastewater using WO3/CNT heterojunction nanocomposite under US and visible light irradiations: A novel hybrid system.

In this paper, in-situ fabrication of tungsten oxide (WO3) on carbon nano-tube (CNT) was performed via sol-gel/hydrothermal method to prepare WO3/CNT nanocomposites and then coupled with visible light and ultrasound (US) irradiations for sono-photocatalytic removal of tetracycline (TTC) and pharmaceutical wastewater treatment. The as-prepared catalysts were characterized by FT-IR, XRD, TEM, UV-VIS DRS, FESEM, EDS, TGA, BET, BJH, EIS, and EDX techniques. The characterization tests, indicated successful incorporation of CTNs into the WO3 framework and efficient reduction of charge carries recombination rate after modifying with CNT. The investigation of experimental parameters verified that 60 mg/L TTC could be perfectly degraded at optimum operational parameters (WO3/CNT: 0.7 g/L, pH: 9.0, US power: 250 W/m2, and light intensity: 120 W/m2 over 60 min treatment. Trapping experiments results verified that HO radicals and h+ were the main oxidative species in degradation of TTC. The as-prepared photocatalysts could be reused after six successive cycles with an approximately 8.8 % reduction in removal efficiency. Investigation of the effect of real pharmaceutical wastewater revealed that this system is able to eliminate 83.7 and 90.6 % of TOC and COD, respectively after 220 min of reaction time. Some compounds with lower toxic impact and molecular weight, compared to raw pharmaceutical wastewater, were detected after treatment by sono-photocatalysis process. The biodegradability of real pharmaceutical wastewater was improved significantly after treatment by WO3/CNT sono-photocatalysis.