We utilized a one-step hydrothermal process for the synthesis of precious metal-doped titanium dioxide (TiO₂)/graphene oxide (GO) composites. The metal-doped TiO₂/GO composites, including silver–TiO₂/GO (Ag–TiO₂/GO), palladium–TiO₂/GO (Pd–TiO₂/GO), and copper–TiO₂/GO (Cu–TiO₂/GO), were synthesized by mixing a metal precursor, titanium butoxide, and graphene oxide in a water–ethanol mixture in an autoclave hydrothermal reactor. The photocatalytic performance of the composites was tested in the photoreduction of carbon dioxide (CO₂) to ethanol. Ag–TiO₂/GO, Pd–TiO₂/GO, and Cu–TiO₂/GO exhibited an ethanol production rate of 109, 125, and 233 μmol/g_cat h, respectively. The outstanding performances of Cu–TiO₂/GO can be attributed to a combined effect of key parameters, including optical band gap, crystallite size, and BET surface area.

Contamination of antibiotics in water is a major cause of antibiotic resistance (ABR) in pathogens that endangers human health and food security worldwide. Ciprofloxacin (CIP) is a synthetic fluoroquinolone (FQ) antibiotic and is reportedly present in surface water at a concentration exceeding the ecotoxicological predicted no-effect concentration in some areas. This study fabricated a CIP sensor using an electropolymerized molecularly imprinted polymer (MIP) of polyaniline (PANI) and poly(o-phenylenediamine) (o-PDA) with CIP recognition sites. The MIP was coated on a reduced graphene oxide (rGO)-modified glassy carbon electrode (rGO/GCE) and operated under a differential pulse voltammetry (DPV) mode for CIP detection. The sensor exhibited an excellent response from 1.0 × 10^-9 to 5.0 × 10^-7 mol L^-1 CIP, showing a sensor detection limit and sensitivity of 5.28 × 10^-11 mol L^-1 and 5.78 μA mol^-1 L, respectively. The sensor's sensitivity for CIP was 1.5 times higher than that of the other tested antibiotics, including enrofloxacin (ENR), ofloxacin (OFX), sulfamethoxazole (SMZ), and piperacillin sodium salt (PIP). The reproducibility and reusability of the sensor devices were also studied.

The harmful effects of antibiotic proliferation on the environment and its persistent nature are urgent global problems. Ciprofloxacin (CIP) is a fluoroquinolone-class antibiotic agent used widely to treat pathogen-related diseases in humans and animals. Its excretion into surface water causes antibiotic resistance in microbes, resulting in difficult-to-treat or untreatable infectious diseases. This study developed a simple and efficient electrochemical sensor to detect CIP. Hydrothermal chemistry was utilized to synthesize an electrophotocatalytic composite of copper-iron mixed metal oxides (CIMMO) on reduced graphene oxide (rGO) (CIMMO/rGO). The composite was employed in an electrochemical sensor and exhibited outstanding performance in detecting CIP. The sensor was operated in differential pulse voltammetry (DPV) mode under light source illumination. The sensor yielded a linear response in the concentration range of 0.75 × 10^-9-1.0 × 10^-7 mol L^-1 CIP and showed a limit of detection (LOD) of 4.74 × 10^-10 mol L^-1. The excellent sensing performance of the composite is attributable to the synergic effects between CIMMO nanoparticles and rGO, which facilitate photoinduced electron-hole separation and assist in the indirect electrochemical reactions/interactions with CIP.

In ethanol production, it is useful to monitor the state of fermentation using a sensor that provides real-time measurement but does not disturb the process. We propose here a tin oxide (SnO2)-reduced graphene oxide (rGO) composite chemiresistive sensor that can be operated on low power and installed in a compact area for the monitoring of ethanol vapor. The sensor exhibited outstanding sensing responses to 29-145 ppm ethanol vapor, providing a sensitivity of 12 ppm-1, a response time of 123 ± 6, recovery time of 128 ± 42 s, and a limit of detection of 3 ppm. The sensor showed good selectivity to ethanol over carbon dioxide, acetic acid and water vapor. The sensing mechanism of the sensor relies on the reaction of ethanol vapor and chemisorbed oxygen species in which the reaction rate increases due to an abundance of the chemisorbed oxygen within n-p heterojunctions of SnO2-rGO.

Polypyrrole (PPy) is a conductive polymer known for its biocompatibility and ease of synthesis. Chemically polymerized PPy was synthesized in the presence of sodium dodecyl sulfate (SDS), showing correlations among chemical properties, physical morphology, and electrical properties. Focused synthesis parameters included the pyrrole (Py) concentration, SDS concentration, and ammonium persulfate (APS)/Py ratio. The addition of SDS during chemical polymerization influenced the physical morphology of PPy by altering the self-assembling process via micelle formation, yielding sheet-like morphologies. However, the phenomenon also relied heavily on other synthesis parameters. Varying SDS concentrations within the 0.01 to 0.30 M window produced PPy sheets with no significant difference in optical band gap or physical size. While using 0.10 M SDS, an increase in Py concentration from 0.10 to 0.30 M yielded a larger size of PPy as the morphology changed from sheet-like to irregular shape. The band gap dropped from 2.35 to 1.10 eV, and the conductivity rose from 6.80 × 10^-1 to 9.40 × 10^-1 S/m. With an increase in the APS/Py ratio, the PPy product changed from a random to a sheet-like form. The product provided a larger average size, a decreased band gap, and increased electrical conductivity. Py polymerization in the absence of SDS revealed no significant change in shape or size as the Py concentration increased from 0.10 to 0.30 M; only a sphere-like form was observed, with a large band gap and small conductivity. Results from Raman spectral analysis indicated a correlation between optical band gap, physical morphology, and bipolaron/polaron ratio, mainly at the wavelengths associated with C-C stretching and C-H deformation. The increase in average size was associated with a decrease in band gap and resistance as well as an increase in the bipolaron/polaron ratio. This work indicates a strong correlation between size, morphology, electrical properties, and the bipolaron/polaron ratio of PPy in the presence of SDS.