Abstract
Graphene-surfactant composite materials obtained by the ultrasonic exfoliation of graphite powder in the presence of ionic surfactants (either CTAB or SDS) were utilised to construct thin films using layer-by-layer (LbL) electrostatic deposition technique. A series of graphene-based thin films were made by alternating layers of either graphene-SDS with polycations (PEI or PAH) or graphene-CTAB with polyanions (PSS). Also, graphene-phthalocyanine composite films were produced by alternating layers of graphene-CTAB with tetrasulfonated nickel phthalocyanine. Graphene-surfactant LbL films exhibited good electric conductivity (about 0.1 S/cm) of semiconductor type with a band gap of about 20 meV. Judging from UV-vis spectra measurements, graphene-phthalocyanine LbL films appeared to form joint π-electron system. Gas sensing testing of such composite films combining high conductivity of graphene with the gas sensing abilities of phthalocyanines showed substantial changes (up to 10%) in electrical conductivity upon exposure to electro-active gases such as HCl and NH 3 .
Highlights
Graphene is one of the most popular materials of modern times with thousands of publications covering all possible aspects of the physical-chemical properties of graphenebased materials and their applications
The second part of this work is dedicated to making graphene-phthalocyanine LbL films and studying their optical and electrical properties including the effect of electro-active gases
In the series of graphene-phthalocyanine samples graphene-cetyl- trimethyl- ammonium bromide (CTAB) was used in alternation with tetrasodium sulphonate nickel phthalocyanine (NiPc-(SO3– Na)4 or shortly NiPc) which chemical structure is shown in figure 1c
Summary
Graphene is one of the most popular materials of modern times with thousands of publications covering all possible aspects of the physical-chemical properties of graphenebased materials and their applications. Our previous study of LB and LbL graphene-surfactant composite films showed high electric conductivity and a temperature dependence of conductivity of semiconductor type (conductivity rising with temperature), though that required further verification. The use of electrostatic LbL deposition offer another attractive possibility of alternating electrically charged graphene layers with other molecular layers, for example phthalocyanines. Metal-phthalocyanines thin films are known by excellent gas sensitivity to electro-active gases though their conductivity is very poor [8]. In the current research we continue studying electric conductivity of graphene-surfactant composite films with particular focus in temperature dependence of conductivity. The second part of this work is dedicated to making graphene-phthalocyanine LbL films and studying their optical and electrical properties including the effect of electro-active gases
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