Application of surface complexation modeling on modification of hematite surface with cobalt cocatalysts: a potential tool for preparing homogeneously distributed catalysts

Abstract

The knowledge required to synthesize homogeneously distributed catalysts on the support surfaces is strongly reliant on understanding the interaction between the catalyst and surface of support, which is identical to the descriptions of interactions between environmental pollutants and adsorbents in the field of environmental chemistry. The connection between catalyst synthesis and environmental chemistry is demonstrated herein by using surface complexation modeling (SCM), whose physical foundation is built on the stoichiometric reaction between one solute and one adsorption site on the surface of adsorbents. As suggested by our simulation and supported by TEM images, the manipulation of either homogeneous distribution or coarse clusters of cobalt cocatalysts over hematite surfaces can be achieved by adjusting the pH and initial Co 2+ concentration. This is attributed to the conversion of adsorbed Co 2+ or Co(OH) 2 precipitates on hematite surfaces. Different surface distributions of cobalt cocatalysts further influence the reactivity of photodegradation of organic dyes and photoelectrochemical reactions, which is strongly dependent on the occurrence of the Fenton reactions or charge transport. Our results not only demonstrate the potential of SCM on guiding the preparation of homogeneously distributed catalysts but also indicate that the abundant amount of knowledge in environmental science could be adopted to design an appropriate protocol for catalyst synthesis.

Understanding the role of phosphate in the photoelectrochemical performance of cobalt-phosphate/hematite electrode systems

“…These randomly deposited Co(OH) 2 precipitates would be thermally converted to Co 3 O 4 catalysts in the subsequent sintering process. 20 Based on our simulations, we note that the initial Co 2+ concentration and solution pH have essential inuences on the distribution of associated Co catalysts over the surface of hematite electrodes. As shown in Fig.…”

“…The stoichiometric reaction between the surface of hematite particles and Co 2+ (SOH + Co 2+ 4 SOCo + + H + ) was considered. 20 As shown in Fig. 1(a) (with 0.1 mM initial Co 2+ ), the cobalt adsorption edge appears at pH 4 and no Co(OH) 2 is found in the system.…”

“…1(a). In both cases, an ultrathin Co 3 O 4 catalyst layer would appear (<5 nm) on the surface of the hematite electrodes, 20 and this explains why the surface morphologies in Fig. 1 environment, a very limited amount of surface Co 3 O 4 catalyst is expected to be associated with the surface of hematite due to the electrostatic repulsion between Co 2+ and hematite.…”

“…Second, as the equilibrium constant is a state function, we adopted the log K a1 as 6.9 for the protonation reaction (eqn (2)) and log K a2 as À12.8 for the deprotonation reaction of hematite (eqn (3)) in accordance with our preliminary study. 20 SOH + H + 4 SOH 2 +…”

Sunlight-driven water splitting using hematite nanorod photoelectrodes

“…Iron is the fourth most common element in the earth's crust composition, which combined with several fundamental characteristics make this widespread mineral attractive for many technological applications including catalysis, optoelectronics, and sensors (Xavier et al 2014, Wang et al 2015b, Bailly et al 2016, Landman et al 2017. It is commonly found in nature in oxide form with four different crystallographic arrangements (such as alpha, beta gamma, and epsilon) (Navrotsky et al 2008, Lavina and Meng 2015, Tuček et al 2015.…”