Correction: Voltammetric pH sensor based on electrochemically modified pseudo-graphite.

Correction for 'Voltammetric pH sensor based on electrochemically modified pseudo-graphite' by Haoyu Zhu et al., Analyst, 2020, 145, 7252-7259, https://doi.org/10.1039/D0AN01405B.

Voltammetric pH sensor based on electrochemically modified pseudo-graphite.

A nanocrystalline graphite-like amorphous carbon (graphite from the University of Idaho thermolyzed asphalt reaction, GUITAR) shares morphological features with classical graphites, including basal and edge planes (BP, EP). However, unlike graphites and other sp2-hybridized carbons, GUITAR has fast heterogenous electron transfer (HET) across its basal planes, and resistance to corrosion similar to sp3-C and boron-doped diamond electrodes. In this contribution, quinoid modified BP-GUITAR (q-GUITAR) is examined as a sensor for pH determination. This modification is performed by applying 2.0 V (vs. Ag/AgCl) for 150 seconds followed by 15 cyclic voltammetric scans from -0.7 to 1.0 V at 50 mV s-1 in 1.0 M H2SO4. The quinoid surface coverage of q-GUITAR is 1.35 × 10-9 mol cm-2, as measured by cyclic voltammetry. X-ray photoelectron spectroscopy analysis also confirms the high surface coverage. The quinoid surface concentration ranks highest in literature when compared with other basal plane graphitic materials. This yields a sensor that responds through a square wave voltammetric reduction peak shift of 63.3 mV per pH over a pH range from 0 to 11. The response on q-GUITAR is stable for >20 measurements and no surface re-activation is required between the measurements. The common interferents, Na+, K+ and dissolved oxygen, have no effect on the response of the q-GUITAR-based pH sensor.

Electrochemical determination of free chlorine on pseudo-graphite electrode.

Pseudo-graphite from the University of Idaho Thermolyzed Asphalt Reaction also known as GUITAR is a new form of carbon. It shares morphological features with graphites, including basal and edge planes. Unlike graphites and other sp2-hybridized carbons, GUITAR has fast heterogeneous electron transfer across its basal planes and resistance to corrosion similar to boron-doped diamond electrodes. In this contribution GUITAR electrodes were examined as sensors for aqueous free chlorine (HOCl and OCl-) at pH 7.0 with cyclic voltammetric (CV) and chronoamperometric (CA) methods. Using CV at 50 mV s-1 GUITAR has a limit of detection of 1.0 µmol L-1, linear range of 0-5,000 µmol L-1, sensitivity of 215.8 µA L mmol-1 cm-2 and a signal stability of 4 days in constant exposure to 1 mmol L-1 free chlorine in pH 7.0, 0.1 mol L-1 phosphate buffer system. After 7 days of exposure GUITAR electrodes lost 37% of the former sensitivity, which was recovered by an in-situ regeneration procedure. The common aqueous ions, Ca2+, Na+, NO3-, SO42-, Cl-, CO32- and dissolved oxygen did not affect the response of the GUITAR-based sensor. The combination of limit of detection, linear range, sensitivity, sensor lifetime and its relative lack of interferences indicate that GUITAR is one of the best performers in free chlorine sensors.

Templated growth of graphenic materials.

A novel strategy is proposed for the topologically controlled synthesis of extended graphenic sheets by additively reacting carbon into a pre-existing graphene sheet which is on top of a templating substrate. This concept is implemented and demonstrated using chemical vapor deposition (CVD). Novel morphological features observed in this study suggest unusual aspects of the CVD growth process. CVD results demonstrate the basic soundness of the synthesis strategy but highlight the sensitivity of the process to certain types of disruption and the need for alternative forms of embodiment.