Fabrication of graphitic-C3N4 quantum dots coated silicon nanowire array as a photoelectrode for vigorous degradation of 4-chlorophenol

Although Si is a successful photovoltaic material, its application in the photoelectrochemical (PEC) field is limited because an insulated SiO2 layer always extends quickly from surface to depth once bare Si contacts with an aqueous solution. To inhibit this oxidation passivation, Si nanowires (SiNWs) were coated with graphitic-C3N4 quantum dots (g-C3N4 QDs) to form SiNWs@g-C3N4 QDs, in which g-C3N4 QDs acted as a protection layer to isolate Si from water and to improve the photogenerated charge transfer. Observed by SEM and TEM, it was confirmed that dispersive g-C3N4 QDs anchored on the surface of SiNWs. PEC performance indicated that the photocurrent of bare SiNWs declined obviously while the photocurrent of SiNWs@g-C3N4 QDs was stable. The photocurrent of SiNWs@g-C3N4 QDs reached 6.7 mA cm (2) at - 1.5 V (vs. SCE) which was 1.6 times higher than that of pristine SiNWs (4.2 mA cm (- 2)). Taking 4-chlorophenol as a target pollutant to investigate the photoelectrocatalytic capability of the SiNWs@g-C3N4 QDs, more than 85% of 4-chlorophenol was successfully removed in 120 min, while the value for SiNWs was only 52.0%. The pseudo-first-order kinetic constant of 4-chlorophenol degradation on SiNWs@g-C3N4 QDs was 2.3 times as great as that on pristine SiNWs. The improved degradation efficiency benefited from the improved stability as well as the enhanced photo-generated charge transfer and separation driven by the built-in electric field at the interface between g-C3N4 QDs and SiNWs. The SiNWs@g-C3N4 QDs will also be useful in other research areas such as water splitting, sensors, etc.