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Cetyltrimethylammonium bromide (CTAB) has been used to enhance the selectivity of CO2 electrochemical reduction. Traditionally, this selectivity was attributed to repulsion of water molecules due to a CTAB self-assembled monolayer, which forms under negative potential and disassembles at positive voltage due to electrostatic repulsions. In this report, using in operando interface sensitivity sum frequency generation spectroscopy, we investigated the self-assembly behavior of CTAB across a broad electrochemical potential range. We observed that CTAB molecules form a stable monolayer at the Stern layer over the entire potential scan, even when the electrodes are positively charged. Rather than disassembling, the CTAB molecules reorient themselves to balance the electrostatic interactions and the non-covalent hydrophobic effects, the latter being the primary driving force maintaining the monolayer at a positive potential. This finding contrasts the traditional view that CTAB monolayers are absent when the electrodes are positively charged, indicating a stable and ordered monolayer with respect to the electrostatic repulsions at liquid/electrode interfaces. The balance between non-covalent and electrostatic interactions offers a facile and reversible electrochemical method to control the local environment and dominating interactions at the Stern layer of the electrode surface, thus providing a means for engineering a micro-electrochemical environment. 

Becauseof thehighdielectricstrengthofwater, it isextremelydifficult todischargeplasmainacontrollablewayin the aqueous phase. By using lithographically defined electrodes andmetal/dielectric nanoparticles, we create electric field enhancementthatenablesplasmadischargeinliquidelectrolytesatsignificantlyreducedappliedvoltages.Here,weusehighvoltage (10−30kV)nanosecondpulse(20ns)dischargestogenerateatransientplasmaintheaqueousphase.Anelectrodegeometrywitha radiusofcurvatureofapproximately10μm,agapdistanceof300μm,andanestimatedfieldstrengthof5×106V/cmresultedina reductionintheplasmadischargethresholdfrom28to23kV.Asecondstructurehadaradiusofcurvatureofaround5μmanda gapdistanceof100μmhadanestimatedfieldstrengthof9×106V/cmbutdidnotperformaswellasthelargergapelectrodes. Addinggoldnanoparticles(20nmdiameter) insolutionfurther reducedthethresholdforplasmadischargeto17kVduetothe electricfieldenhancementatthewater/goldinterface,withanestimatedE-fieldenhancementof4×.Addingaluminananoparticles decoratedwithPtreducedtheplasmadischargethresholdto14kV. Inthisscenario, theemergenceofatriplepointatthejuncture ofalumina,Pt,andwaterresultsinthecoexistenceofthreedistinctdielectricconstantsatasingularlocation.Thisleadstoanotable concentrationof electric field, effectively aiding in the initiationof plasma discharge at a reduced voltage. To gain amore comprehensive and detailed understanding of the electric field enhancement mechanism, we performed rigorous numerical simulations.Thesesimulationsprovidevaluableinsights intotheintricateinterplaybetweenthelithographicallydefinedelectrodes, thenanoparticles, andthe resultingelectricfielddistribution, enablingus toextract crucial informationandoptimize thedesign parameters forenhancedperformance. 

This study evaluates the beneficial effects of discharging nanosecond pulse transient plasma (NPTP) in a coaxial electrostatic precipitator for capturing nanoscale soot particles (∼50 nm) produced by an ethylene flame. 

Detection of illicit drug residues from wastewater provides a new route toward community-level assessment of drug abuse that is critical to public health. However, traditional chemistry analytical tools such as high-performance liquid chromatography in tandem with mass spectrometry (HPLC-MS) cannot meet the large-scale testing requirement in terms of cost, promptness, and convenience of use. In this article, we demonstrated ultra-sensitive and portable surface-enhanced Raman scattering sensing (SERS) of fentanyl, a synthetic opioid, from sewage water and achieved quantitative analysis through principal component analysis and partial least-squares regression. The SERS substrates adopted in this application were synthesized by in situ growth of silver nanoparticles on diatomaceous earth films, which show ultra-high sensitivity down to 10 parts per trillion in artificially contaminated tap water in the lab using a commercial portable Raman spectrometer. Based on training data from artificially contaminated tap water, we predicted the fentanyl concentration in the sewage water from a wastewater treatment plant to be 0.8 parts per billion (ppb). As a comparison, the HPLC-MS confirmed the fentanyl concentration was below 1 ppb but failed to provide a specific value of the concentration since the concentration was too low. In addition, we further proved the validity of our SERS sensing technique by comparing SERS results from multiple sewage water treatment plants, and the results are consistent with the public health data from our local health authority. Such SERS sensing technique with ultra-high sensitivity down to sub-ppb level proved its feasibility for point-of-care detection of illicit drugs from sewage water, which is crucial to assess public health.