To overcome the limitations of metal-organicf rameworks (MOFs) for catalysis (e.g.,l ow catalytic activities resulting from blockageo ft he active metal centers by organic linkers) is of great importance.H erein, we demonstratet he formation of UiO-66 nanoparticles with ultrasmall size and linker defects with the aid of SnS 2 nanosheets.T he UiO-66 nanoparticles supported by SnS 2 nanosheets were found to exhibit excellent catalytic activity for the cycloaddition reactiono fC O 2 with propylene oxide under solvent-freea nd co-catalyst-free conditions. Outstandingly,t he catalytic activity was 11 times highert han that of the pure UiO-66 catalystu nder optimum conditions. We thus provide ap romisingr oute to modify MOF particles thus to promote their catalytic performance.The chemical fixation of carbond ioxide (CO 2 )i sa ni mportant way to solve the increasing amounto fC O 2 in the atmosphere. [1] Among the diverse kinds of chemical fixationr outes, the cycloadditiono fC O 2 to cyclic carbonatesh as attracted much attentiono wing to its 100 %a tom efficiency and the wide applications of cyclic carbonatesi nl ithium batteries, [2] as intermediates of chemical reactions, [3] as polar aprotic solvents, [4] and in fine chemicals. [5] Up to now,alot of catalysts have been used in cycloadditionr eactions of CO 2 ,s uch as metal-salen complexes, [6] ionic liquids, [7] lanthanide oxychloride, [8] functional polymers, [9] andm etal-organic frameworks (MOFs). [10] Particularly,M OFs have been regardeda sc atalysts with great potential for the CO 2 cycloaddition reactiono wing to their unique features, which include high surface areas and porosities, gas adsorption abilities, andm anyr eactive metal sites. [11][12][13][14][15][16][17] However,t he catalytic activities of MOFs are largely restricted mainly because of blockage of the active metal centers by organic linkers. Co-catalysts,f or example, cetyltrimethylammonium bromide, [18] phenyltrimethylammonium tribromide, [19] and tetrabutylammoniumb romide, [20] are usually requisite, which inevitably increase the economicb urden and postprocessing complexity.I tiso fg reat importance to develop heterogeneous MOFs catalysts with desirable structuresf or high-performance CO 2 chemical fixation, promisingly under mild and environmentally benign conditions (e.g.,s olventf ree, no co-catalyst, etc.).Herein, we propose for the first time the utilization of tin sulfide (SnS 2 ), which has an ultrathin 2D nanostructure, narrow band gap of 2.36 eV,a nd good stability,f or regulating the particle size, structure, and properties of MOFs. By as olvothermal route for MOF synthesis in the presence of SnS 2 ,U iO-66 [Zr 6 O 4 (OH) 4 (BDC) 6 ,B DC = 1,4-benzenedicarboxylate] nanoparticles can be downsized from approximately 100 nm (in the absence of SnS 2 )t o1 0-30 nm. It is interesting that the as-synthesized small nanoparticles of UiO-66p resent highly exposed ZrÀ Oc lusters for the exposure of more catalytically active metal sites. Owing to these uniquef eatures, the UiO-66 nanopartic...