Synthesis And Characterization Based On Low Dimensional Nanocomposites Of Cu₂O And CH₃NH₃PbBr₃

Nanomaterials have made great progress in last decade and been widely applied in photoelectrical application, sensor, energy and catalysis due to their unique physical and chemical properties. However, the fast development of society demands better performance of nanomaterials. Single nanomaterial always has some drawbacks which cannot be avoided. Therefore, nanocomposites have attracted tremendous attention because the advantages of nanocomposites can be amplified and shortcomes can be avoided.In this paper, Cu₂O/Cu, CH₃NH₃PbX₃/SiO₂, CH₃NH₃PbX₃/peptide and CH₃NH₃PbX₃/g-C₃N₄ nanocomposites were fabricated through electrodeposition and crystallization methods, respectively. The electrical properties of Cu₂O/Cu nanocomposites were investigated and Cu₂O/Cu nanocomposites was used to constructed the electrochemical sensor for the detection of H₂O₂. The optical properties, morphology, stability and capping mechanism of CH₃NH₃PbX₃/SiO₂, CH₃NH₃PbX₃/ peptide and CH₃NH₃PbX₃/g-C₃N₄ nanocomposites were also studied in detail. The main results are listed below:?1? Cu₂O/Cu nanocomposites were successfully prepared using electrodeposition method. The main composition is Cu nanocubes?CuNCs? when the pH value, temperature, electrodepositon time and voltage are 4.5, 60 ?, 1 h and-0.2 V, respectively. The important parameters?including reaction temperature, pH and reaction time? have been investigated in detail. It has been revealed that both the size of Cu nanocubes and the content of Cu₂O increased when increasing electrodepositon time and temperature of electrolyte. It has also been demonstrated that the pH value has a great influence on the growth of Cu₂O due to the reaction between Cu₂O and protons. When increasing the pH value of electrolyte, Cu nanocubes were transformed into triangular Cu₂O nanocrystals gradually.?2? Cu₂O/CuNC nanocomposites have been used to construct an electrochemical sensor for detection of hydrogen peroxide. The effects of deposition time and pH were investigated in detail. It was found that the sensor has the highest sensitivity to H₂O₂ when the pH value of electrolyte is 4.5 and electrodeposition time is 30 min. The Cu₂O/Cu NC modified electrode exhibits a fast response time?³ s?, a wide linear dependence?R = 0.996? at a concentration of H₂O₂ from 4.0 × 10-7 M to 1.0 × 10-2 M, a high sensitivity of 870.4 m A·m M-1·cm-2 and a detection limit of 2.0 × 10-7 M. Additionally, the sensor was successfully applied for the determination of H₂O₂ in milk and the recovery is over 90%.?3? Organolead bromide CH₃NH₃PbBr₃ perovskite nanocrystals?PNCs? with green photoluminescence?PL? have been synthesized using two different aliphatic ammonium capping ligands, octylammonium bromide?OABr? and octadecylammonium bromide?ODABr?, respectively. Morphological studies determined that the PNCs exhibit average particle size 3.9 ± 1.0 nm for PNCOABr and 6.5 ± 1.4 nm for PNCODABr. The main PL peaks are located at 513 and 529 nm for PNCOABr and PNCODABr, respectively. The quantum yield?QY? can reach up to ²0% for PNCOABr, which is two times larger than that of PNCODABr?10%?. The PL peak of PNCs can be varied from 441 to 553 nm by adjusting the amount of Cl or I. Moreover, the stability of PNCs is much better than CH₃NH₃PbBr₃ bulk material due to the passivation of PNCs by straight capping ligands.?4? CH₃NH₃PbBr₃ PNCs of different sizes?².5–100 nm?, tunable fluorescence?452-524 nm? with high PL QY?55%? and product yield have been synthesized using the branched molecules, APTES and NH2-POSS, as capping ligands. These ligands are sterically hindered, resulting in a uniform size of PNCs. The different capping effects resulting from branched versus straight-chain capping ligands were compared and a possible mechanism were proposed to explain the dissolution–precipitation process. Unlike conventional PNCs capped with straight-chain ligands, APTES-capped PNCs show high stability in protic solvents as a result of the strong steric hindrance and propensity for hydrolysis of APTES, which prevent such molecules from reaching and reacting with the core of PNCs?5? The well-passivated PNCs can only be obtained when both amino and carboxylic groups were involved, and this is attributed to the protonation reaction between –NH2 and –COOH that is essential for the passivation of Br and Pb defect, respectively. To better understand this synergistic effect, peptides with different lengths have been studied and compared. The product yield can reach up to ⁴4%. Furthermore, the size of PNCspeptide can be varied from ³.9 to 8.6 nm by adjusting the concentration of the peptide, resulting in tunable optical properties due to the quantum confinement effect. In addition, Cs Pb Br3 PNCs were also synthesized with peptides as capping ligands, further demonstrating the generality and versatility of this strategy.?6? Protonated graphitic-C₃N₄?p-g-C₃N₄? has been firstly studied as a capping ligand for the surface passivation of PNCs. It was found that the protonation process resulted in smaller g-C₃N₄ particles and more amino terminal groups. In contrast to pristine g-C₃N₄, p-g-C₃N₄ induced the formation of sheet-like PNCs with a few layers?1-6? in thickness due to the interaction between the –NH3+ terminals of p-g-C₃N₄ and the surface defects of CH3NH3 Pb Br3 PNCs. With increasing concentration of p-g-C₃N₄, the resultant PNCs became thinner and presented layer-dependent optical properties owing to the strong quantum confinement effect on this scale. Moreover, the fluorescence intensity of PNCs decreases when increasing the concentration of p-g-C₃N₄, which may result from the electron transfer between PNCs and p-g-C₃N₄.