Synthesis, characterization and catalytic tests of new siloxane-containing MOFs. Alkaline decomposition of hydrogen peroxide with 90% conversion after 30 min. Unprecedented catalytic activity in photodecomposition of Congo red under sunlight. Discoloration efficiency of 82% after 80 min with MOF alone and 97% with H2O2 added. Cleaner water results when the MOFs are used without addition of H2O2.