Activity of Cadmium Sulfide Photocatalysts for Hydrogen Production from Water: Role of Support

Photosensitive Thin Films Based on Drop Cast and Langmuir-Blodgett Hydrophilic and Hydrophobic CdS Nanoparticles

Comparative photoelectrochemical studies of cadmium sulfide (CdS) nanoparticles with either hydrophilic or hydrophobic surface properties are presented. Oleylamine organic shells provided CdS nanoparticles with hydrophobic behavior, affecting the photoelectrochemical properties of such nanostructured semiconductor. Hydrophilic CdS nanoparticles were drop-cast on the electrode, whereas the hydrophobic ones were transferred in a controlled manner with Langmuir-Blodgett technique. The substantial hindrance of photopotential and photocurrent was observed for L-B CdS films as compared to the hydrophilic, uncoated nanoparticles that were drop-cast directly on the electrode surface. The electron lifetime in both hydrophilic and hydrophobic nanocrystalline CdS was determined, revealing longer carrier lifetime for oleylamine coated CdS nanoparticles, ascribed to the trapping of charge at the interface of the organic shell/CdS nanoparticle and to the dominant influence of the resistance of the organic shell against the flux of charges. The “on” transients of the photocurrent responses, observed only for the oleylamine-coated nanoparticles, were resolved, yielding the potential-dependent rate constants of the redox processes occurring at the interface.

Tetracycline Photocatalytic Degradation under CdS Treatment

Industrialization and the growing consumption of medicines leads to global aquatic contamination. One of the antibiotics widely used against bacterial infections in both human and veterinary medicine is tetracycline. Despite its positive antibiotic action, tetracycline is resistant against degradation, and therefore it accumulates in the environment, including the aquatic environment, creating great health hazards, possibly stimulating antibiotic resistance of pathogenic organisms. In this research, aqueous suspensions of semiconductor nanoparticles CdS were used for photocatalytic activity studies in the presence of methylene blue as a model compound, and finally, in the presence of tetracycline, a broad-spectrum antibiotic widely used against bacterial infections, as well as a live-stock food additive. The mechanism and kinetic rate constants of photocatalytic degradation processes of methylene blue and tetracycline were described in correlation with the energy diagram of CdS nanoparticles.

State Estimation Based on Nonlinear Observer for Hydrogen Production in a Photocatalytic Anaerobic Bioreactor

Hydrogen concentration in a photocatalytic continuous bioreactor was estimated. For the above system, a novel kinetic model of the sulfate-reducing process for hydrogen production was proposed and experimentally confirmed. In addition, we present the design of an estimator based on nonlinear observer, which is robust against modeling errors, to estimate the observable states of the bioreactor. Sulfate, biomass, sulfide, carbon dioxide, cadmium in liquid, cadmium sulfide, and hydrogen concentrations were estimated in spite of errors in the evaluation of the parameters using sulfate concentration as measurable output. The convergence of the proposed observer was analyzed using Lyapunov stability theory. Finally, maximum hydrogen production was 225 mL and 175 mL for batch and continuous processes, respectively.

Shape-Dependent Photocatalytic Activity of Hydrothermally Synthesized Cadmium Sulfide Nanostructures

The effective surface area of the nanostructured materials is known to play a prime role in catalysis. Here we demonstrate that the shape of the nanostructured materials plays an equally important role in their catalytic activity. Hierarchical CdS microstructures with different morphologies such as microspheres assembled of nanoplates, nanorods, nanoparticles, and nanobelts are synthesized using a simple hydrothermal method by tuning the volume ratio of solvents, i.e., water or ethylenediamine (en). With an optimum solvent ratio of 3:1 water:en, the roles of other synthesis parameters such as precursor's ratio, temperature, and precursor combinations are also explored and reported here. Four selected CdS microstructures are used as photocatalysts for the degradation of methylene blue and photoelectrochemical water splitting for hydrogen generation. In spite of smaller effective surface area of CdS nanoneedles/nanorods than that of CdS nanowires network, the former exhibits higher catalytic activity under visible light irradiation which is ascribed to the reduced charge recombination as confirmed from the photoluminescence study.

One-Step Synthesis and Structural Features of CdS/Montmorillonite Nanocomposites

A novel synthesis method was introduced for the nanocomposites of cadmium sulfide and montmorillonite. This method features the combination of an ion exchange process and an in situ hydrothermal decomposition process of a complex precursor, which is simple in contrast to the conventional synthesis methods that comprise two separate steps for similar nanocomposite materials. Cadmium sulfide species in the composites exist in the forms of pillars and nanoparticles, the crystallized sulfide particles are in the hexagonal phase, and the sizes change when the amount of the complex for the synthesis is varied. Structural features of the nanocomposites are similar to those of the clay host but changed because of the introduction of the sulfide into the clay.