Photoinduced electron transfer in aqueous carbon nanotube/block copolymer/CdS hybrids: Application in the construction of photoelectrochemical cells

Pristine and shorted multi-walled carbon nanotubes (pMWCNT and sMWCNT, respectively) non-covalently modified with a block copolymer (poly[sodium (2-sulfamate-3-carboxylate) isoprene-b-styrene] - abbreviated as CSI) are used for the formation of CdS semiconductor nanohybrids. The CdS nanoparticles are preferentially localized on the surface of the nanotubes due to specific interactions with the polymer chains. In these nanohybrid materials photoinduced electron transfer phenomena are found to occur from the photoexcited CdS nanoparticles to the nanotubes as evidenced by the efficient fluorescence emission quenching of CdS nanoparticles. Nanosecond transient absorption spectroscopy sheds light on the transient species formed by charge separation, namely (pMWCNT)^-/CSI/(CdS)⁺ and (sMWCNT) ^-/CSI/(CdS)⁺. The MWCNT/CSI/CdS nanohybrid materials are deposited onto ITO electrodes by the drop-casting method. The ITO/sMWCNT/CSI/CdS electrode exhibit an incident photon to photocurrent efficiency (IPCE) of 7% at an applied bias of +0.2 V vs. SCE in a standard three-compartment electrochemical cell. Direct electron injection from the reduced nanotubes to ITO electrode after the photoinduced charge separation is responsible for the photocurrent generation.