Photocatalytic water splitting H 2 production based on semiconductor nanoparticle heterojunctions is an attractive strategy. Various morphologies of Zn(OH)F have been widely used in photocatalytic degradation of organic matter; however, its application in photocatalytic hydrogen production has been rarely reported. Herein, two kinds of morphologies catalysts, one rodlike CdS/Zn(OH)F (CdS/ RZF) and the second flower-like heterojunction CdS nanoparticle/ Zn(OH)F (CdS NP/FZF), were prepared by the simple and mild hydrothermal method. Interestingly, CdS NP/FZF exhibited superior photocatalytic activity to CdS/RZF due to the flower-like structure of Zn(OH)F, which prevented the aggregation of CdS nanoparticles, thereby exposing more active sites. Notably, the light absorption ability of CdS nanoparticle/Ni x Zn 1−x (OH)F (CdS NP/NZF) was greatly improved, which was due to the introduction of Ni 2+ . As a result, the H 2 production rate of CdS NP/NZF (2410 μmol•g −1 •h −1 ) was increased by 2.19 times compared to that of CdS NP/FZF. This remarkable enhancement of photocatalytic H 2 -evolution activity of CdS NP/NZF was attributed to its special morphology in addition to Ni 2+ doping, which promoted the separation of photogenerated electrons and holes, as well as improved the ability of visible-light response. This work provides a family of catalysts as a promising candidate for photocatalytic hydrogen evolution.

Pepsin was used to effectively degrade chitosan in order to make it more useful in biotechnological applications. The optimal conditions of enzymolysis were investigated on the basis of the response surface methodology (RSM). The structure of the degraded product was characterized by degree of depolymerization (DD), viscosity, molecular weight, FTIR, UV-VIS, SEM and polydispersity index analyses. The mechanism of chitosan degradation was correlated with cleavage of the glycosidic bond, whereby the chain of chitosan macromolecules was broken into smaller units, resulting in decreasing viscosity. The enzymolysis by pepsin was therefore a potentially applicable technique for the production of low molecular chitosan. Additionally, the substrate degradation kinetics of chitosan were also studied over a range of initial chitosan concentrations (3.0~18.0 g/L) in order to study the characteristics of chitosan degradation. The dependence of the rate of chitosan degradation on the concentration of the chitosan can be described by Haldane’s model. In this model, the initial chitosan concentration above which the pepsin undergoes inhibition is inferred theoretically to be about 10.5 g/L.

As a means of making chitosan more useful in biotechnological applications, it was hydrolyzed using pepsin, chitosanase and α-amylase. The enzymolysis behavior of these enzymes was further systematically studied for its effectiveness in the production of low-molecular-weight chitosans (LMWCs) and other derivatives. The study showed that these enzymes depend on ion hydronium (H 3 O + ), thus on pH with a pH dependence fitting R 2 value of 0.99. In y = 1.484[H + ] + 0.114, the equation of pH dependence, when [H + ] increases by one, y (k 0 /k m ) increases by 1.484. From the temperature dependence study, the activation energy (E a ) and pre-exponential factor (A) were almost identical for two of the enzymes, but a considerable difference was observed in comparison with the third enzyme. Chitosanase and pepsin had nearly identical E a , but α-amylase was significantly lower. This serves as evidence that the hydrolysis reaction of α-amylase relies on low-barrier hydrogen bonds (LBHBs), which explains its low E a in actual conditions. The confirmation of this phenomenon was further derived from a similarly considerable difference in the order magnitudes of A between α-amylase and the other two enzymes, which was more than five. Variation of the rate constants of the enzymatic hydrolysis of chitosan with temperature follows the Arrhenius equation.