Fabrication of lithium silicates from zeolite for CO2 capture at high temperatures

Li4Si O4 has been regarded as one of the most promising high-temperature CO2 sorbents.However,for practical applications,its CO2sorption kinetics,cycling stability and sorption properties at lower temperatures or lower CO2 concentrations have to be improved.In this contribution,four Li4Si O4 sorbents were synthesized from zeolite precursors MCM-41,MCM-48,TS-1,and ZSM-5.The CO2 uptake,cycling stability and the optimal CO2 sorption conditions were investigated.Among the samples,MCM-41-Li4Si O4 showed the best cycling stability at 650°C,with a stable reversible CO2 uptake of 29.1 wt%under 100 vol%CO2 during 20 cycles.But its sorption kinetics and CO2 uptakes at lower temperatures and lower CO2 concentrations need to be improved.We then demonstrated that the sorption kinetics can be improved by modifying the MCM-41 precursor with metals such as Al,Ti,Ca,and Na.The Na-MCM-41-Li4Si O4 sample exhibited the highest sorption rate,and reached the equilibrium sorption capacity close to the theoretical value of 36.7 wt%within 20 min.In addition,we proved that coating the MCM-41-Li4Si O4with Na2CO3and K2CO3can significantly increase the CO2uptakes at lower temperatures(e.g.550℃)and lower CO2concentrations(10–20 vol%).At 550℃ and under 20 vol%CO2,15 wt%K2CO3-MCM-41-Li4Si O4 and 10 wt%Na2CO3-MCM-41-Li4Si O4 sorbents resulted in a CO2 uptake of 32.2 wt%and 34.7 wt%,respectively,which are much higher than that of MCM-41-Li4Si O4(11.8 wt%).These two sorbents also showed good cycling stability.The promoiting mechasnim by alkali carbonate coating was discussed by a doubleshell model.

Conservative endodontic management using a calcium silicate bioceramic sealer for delayed root fracture:A case report and review of the literature

BACKGROUND The success rate of conservative endodontic management for root fracture varies greatly based on different methods used.It has been rarely reported that calcium silicate-based materials are applied in root fracture treatment.CASE SUMMARY A 38-year-old male patient presented with spontaneous pain from the upper left anterior teeth for 1 wk.The spontaneous pain was subsequently relieved,but pain on mastication persisted for 3 d.The patient had a dental trauma from a boxing match 15 years ago.Cone beam computed tomography showed that the maxillary left central incisor had oblique fracture lines and a radiolucent lesion around the fracture line.The tooth was diagnosed with an oblique root fracture with no healing and symptomatic apical periodontitis.In the following conservative endodontic management,the coronal and apical fragments of the canal both were chemo-mechanically prepared and obturated using a single cone gutta-percha with iRoot SP(Innovative BioCreamix Inc,Vancouver,Canada),a new calcium silicate-based bioceramic root canal sealer.At follow-ups at 1,6,12,and 24 mo,the patient was asymptomatic and the radiolucency around the fracture line was healing radiographically.CONCLUSION Conservative root canal treatment is an alternative treatment in some cases of oblique root fracture with no healing.The application of bioceramic sealers and single core obturation techniques may also be essential to obtain an excellent outcome.