Conducting poly(o-toluidine) (POT)/titanium dioxide (TiO2) nanocomposite films have been synthesized by in situ chemical oxidation polymerization of o-toluidine in the presence of TiO2 nanoparticles. The nanocomposite films were characterized by Fourier transform infrared (FT–IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The characterization results confirmed the polymerization of o-toluidine and the strong interaction between POT and TiO2 nanoparticles. The humidity-sensing property of the films was tested by measuring the direct current electric resistance at two relative humidity (RH) values, 11 and 97 %, respectively. The POT/TiO2 nanocomposite films exhibited quick response and recovery times, which were about 38 and 6 s, respectively. Both the response and recovery time are faster than those of pure POT films. The results indicate that the POT/TiO2 nanocomposite films have better sensing property than pure POT films. The increasing humidity sensitivity of the POT/TiO2 nanocomposite films attributes to the synergic adsorption of the water molecules from both POT and TiO2, and the high surface areas of nanocomposite films.

•Raman vibration modes and SERS characteristic peaks of 5-A-2MBI were assigned.•The molecular electrostatic potential (MEP) of 5-A-2MBI was used to discuss the possible adsorption behavior of 5-A-2MBI.•The SERS detection limit of 5-A-2MBI was 5 × 10− 7` mol·L− 1.5.Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) simulations were employed to study 5-amino-2-mercaptobenzimidazole (5-A-2MBI) molecules. Ag colloids were used as SERS substrates which were prepared by using hydroxylamine hydrochloride as reducing agent. Raman vibration modes and SERS characteristic peaks of 5-A-2MBI were assigned with the aid of DFT calculations. The molecular electrostatic potential (MEP) of 5-A-2MBI was used to discuss the possible adsorption behavior of 5-A-2MBI on Ag colloids. The spectral analysis showed that 5-A-2MBI molecules were slightly titled via the sulfur atoms adhering to the surfaces of Ag substrates. The obtained SERS spectral intensity decreased when lowering the 5-A-2MBI concentrations. A final detection limit on the concentration of 5 × 10− 7 mol · L− 1 was gained. SERS proved to be a simple, fast and reliable method for the detection and characterization of 5-A-2MBI molecules.The SERS spectra of 5-A-2MBI were clearly obtained. The spectral intensities increased with increasing 5-A-2MBI concentrations. The detection limit of 5-A-2MBI was 5 × 10− 7 mol · L− 1. The SERS proved to be a simple, fast and reliable method for the detection and characterization of 5-A-2MBI.

•Ag/TiO2NTs compound nanostructures were fabricated.•The photodegradation of R6G on Ag/TiO2NTs was assessed by SERS.•Good self-cleaning and spectral recovery characters were shown on these substrates.A method for the investigation of photocatalytic degradation of organic molecules adsorbed on the surface of a compound nanostructure, silver nanoparticle (Ag NP) modified titania nanotubes (TiO2NTs), namely Ag/TiO2NTs, was proposed. The method was applied to the photocatalytic degradation of rhodamine 6G (R6G) dye molecules in order to determine its effectiveness. The surface-enhanced Raman scattering (SERS) technique was employed to monitor the photodegradation processes on these bifunctional nanostructures. The photocatalytic characteristic was attributed to the TiO2NTs; however, the SERS activity was caused by the Ag NPs. The Ag/TiO2NTs were able to detect R6G molecular probes with concentration down to 10−8 M. The substrates could not only degrade the adsorbates, but also discard them off under ultraviolet irradiation owing to the high photocatalytic activity of TiO2. Thus, the substrates were able to self-clean and be reused for a new SERS detection cycle. The photodegradation and SERS results revealed that Ag/TiO2NTs acted as promising candidates for photocatalytic activity and SERS substrates; and exhibited high recyclability in the detection of organic molecules. The optimized SERS-active substrates were then employed to study the photodegradation of R6G. The photodegradation kinetics analysis was assessed by selecting the strongest SERS peaks which indicated that the kinetics of the photodegradation of R6G followed the pseudo-first order reaction. Finally, the results presented herein demonstrated that the fabricated Ag/TiO2NTs nanostructures were remarkably suitable as photocatalytically active SERS substrates. Further, the substrates could be effectively utilized for highly sensitive in situ monitoring of the surface photodegradation processes of organic molecules and could be recycled in a more environmentally sustainable manner.

•CdTe QDs modified PS spheres with Ag NP caps were obtained.•A site-selective deposition effect was introduced.•Both fluorescence and SERS properties were investigated.A simple but versatile technique of layer-by-layer self-assembly was used on polystyrene (PS) colloidal templates to produce CdTe quantum dots (QDs) modified PS spheres with Ag nanoparticle (NP) caps. The templates were obtained by self-assembly of monodispersed suspension of PS spheres (700 nm) on glass slides. CdTe QDs and Ag NPs were deposited on PS spheres through electrostatic force with a media layer of poly(diallyldimethyl-ammonium chloride) (PDDA) polyelectrolyte. A novel and interesting site-selective deposition effect of NPs with different sizes on PS spheres was introduced. The small size NPs of CdTe QDs (3 nm) were deposited on the outer surfaces of the PS templates. But the big size NPs of Ag NPs (45 nm) were only deposited on the top surfaces of the PS templates. This site-selective deposition effect benefited from the uniform microporous structures of the monolayer PS templates, which served as sieves to filter the NPs. Only small NPs like CdTe QDs can go through the pathways of the micropores of the PS templates. Big NPs like Ag NPs cannot go through the uniform pores due to the steric hindrance effect. Finally, CdTe QDs modified PS spheres with Ag NPs caps were obtained. It was a new class of dual-function microspheres with applications both in fluorescence and in surface-enhanced Raman scattering (SERS). The morphology and structure of the microspheres were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The fluorescence and SERS properties were obtained by confocal fluorescence microscopy and Raman spectroscopy.

•SAMs of MPTS were used as templates to induce the nucleation and growth of Ba(NO3)2 microcrystals.•The soaking direction was found to play an important role in the crystal growth.•Square-like and triangular-like microcrystals were obtained separately.•The Raman intensity of the (111) facet is five times that of the (100) facet.Self-assembled monolayers (SAMs) of (3-mercaptopropyl)trimethoxysilane (MPTS) were used as templates to induce the nucleation and growth of Ba(NO3)2 microcrystals. X-ray diffraction (XRD) patterns and optical microscopy images were employed to investigate the crystallinity and morphology of the microcrystals. It is interesting that the soaking direction of the templates plays an important role in the crystal growth process. When the MPTS-modified substrates were soaked in a vertical manner, square-like microcrystals with the (100) orientation were synthesized; however, when the substrates were soaked in a horizontal manner, triangular-like microcrystals with the (111) orientation were obtained. These differences may be due to the different regulatory mechanisms involved in the modulation of the crystal growth by the SAMs. These mechanistic discoveries pave a new way to control and design new crystals. Another interesting phenomenon is that the Raman intensity of the (111) facet of the triangular Ba(NO3)2 microcrystals is five times that of the (100) facet. By using this difference, the crystal facet index can be rapidly determined.