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The binary xerogels TiO2–SiO2 are widely used as catalysts and their carriers in organic synthesis. Characterization and adjustment of the electrostatic properties of the surface and the local acidity inside the pores, are necessary for the further development of TiO2–SiO2 xerogels applica-tions. This research investigates acid–base equilibria in the pores, and the surface electrostatic potential (SEP) of binary TiO2–SiO2 xerogels, by the EPR of stable pH‐sensitive nitroxide radicals. These radicals are small enough to penetrate directly into the pores, and to be adsorbed onto the surface of the material under study. This makes it possible to obtain valuable information on the acidic and electrosurface properties of the studied system. The highest negative surface electrical charge asso-ciated with surface electrical potential (SEP) was equal to –196 ± 6 mV. It was induced by the surface of the sample with a 7% TiO2 content. Тhe local acidity inside the pores of this sample was found to be higher, by approximately 1.49 pH units, as compared to that in the external bulk solution. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Funding: D.O.A., E.G.K., D.P.T. acknowledge the financial support from the Russian Foundation for Basic Research (RFBR) grant 18‐29‐12129mk, I.A.K. acknowledges support from the Ministry of Sci‐ ence and Education of the Russian Federation grant No. 14.W03.31.0034 for the nitroxide synthesis.

A spin pH probe technique was used to study the influence of the channel diameter on the EPR spectra of pH-sensitive nitroxide radicals (NR) located in the channels of the mesoporous molecular sieves MCM-41 and SBA-15 with diameters ranging from 2.3 to 8.1 nm. From EPR spectra analysis and the results of the NR retention by the mesoporous molecular sieves upon washing with an aqueous KCl solution, the regularities of NR molecular location inside the channels were studied. The obtained dependence of the fraction of the radical molecules in the fast motional regime (with the rotational correlation times, τc = 2 × 10-11 s-9 × 10-11s) in the channels of the mesoporous molecular sieves as a function of pH indicates that both NR in the fast and slow motional regime (with τc = 8 × 10 -9s-7 × 10-10s) may be used for estimation of the solution acidity inside the channels and of the near-surface electrical potential. © 2013 Elsevier Inc. All rights reserved. This work was supported by the Research Program of the Ministry of the Education of the Russian Federation (2007-2011). E.G.K. thanks the Program of Cooperation “Mikhail Lomonosov” between the Ministry of Education of Russian Federation and the German Service of Academic Exchanges (DAAD). We are grateful to Dr. G. Chandrasekar for assistance in the synthesis of MMS and their characterization. Appendix A

Some of the most important parameters of mesoporous materials are Stern potential of double electrical layer (DEL) and surface charge because of the pivotal role they play in the adsorption of charged molecular species. There are not any conventional and easy-to-perform techniques used to measure Stern potential in porous systems. The purpose of this work is to measure Stern potential in a specific case, i.e., practically cylindrical nanosized hydrated channels of the mesoporous molecular sieves (MMS) MCM-41 and SBA-15 with channel diameters ranging from 2.3 to 8.1 nm using pH-sensitive nitroxide radicals (NR). A technique for direct measurement of the near-surface (Stern) potential using pH-sensitive NR was developed. Negative and positive values of Stern potential for the positively and negatively charged surface of MMS channels were found. The ranges of pH of external solution for the near-zero charge, boost-charging of the channel surface and for dissociation of functional groups in the MMS studied were found. © 2014 Elsevier Inc. All rights reserved. This work was supported by the Russian Foundation for Basic Research (Grant 14-03-00898 ) and by the State task of the Ministry of Education (RF) No 4.1626.2014/K. The experiments were conducted at the Technical University of Kaiserslautern within the Program of Cooperation “Mikhail Lomonosov” between the Ministry of Education of Russian Federation and the German Service of Academic Exchanges (DAAD). Appendix A

Composite materials (CMs) based on zirconia xerogels and powdered cellulose (PC) were synthesized. The effect of the CM surface charge on their complexing properties with respect to Cu2+ ions and on the catalytic activity of the samples in model reactions of the decomposition of H2O 2 and the oxidative dehydrogenation of trimethylhydroquinone with atmospheric oxygen was analyzed. It was experimentally proved that the use of PC for the synthesis of ZrO2-based CMs, as in the case of previously studied CMs based on SiO2 and TiO2, leads to an increase in the specific surface area Ssp and a decrease in the negative electric potential of their surface. The surface charge, sorption method, and the composition of the buffer solution used for sorption have a significant effect on the copper(II) content in the CM phase, the distribution pattern, and the composition of the sorbed copper(II) compounds and on the catalytic activity of the synthesized Cu2+-containing CMs. © Pleiades Publishing, Ltd., 2014. This work was supported by the Russian Foundation for Basic Research, (project no. 14 03 00898) and Program 211 of the Government of the Russian Federation (grant no. 02.03.21.0006).