Confinement and passivation of perovskite quantum dots in porous natural palygorskite toward an efficient and ultrastable light-harvesting system in water

Perovskite quantum dots (QDs) are promising as representative candidates to construct next-generation superior artificial light-harvesting systems (ALHSs). However, their high sensitivity to external environments, especially to water, imposes a stringent limitation for their actual implementation. Herein, by interface engineering and encapsulation with natural palygorskite (PAL), a water-resistant light-harvesting CsPbBr3@PAL antenna was prepared. Molecular dynamics simulations further confirm a significant shielding protection of the PAL matrix to CsPbBr3, facilitating exceptional stability of the CsPbBr3@PAL antenna when exposed to air for 10 months, to 150 °C thermal stress, and even to water for more than 30 days, respectively. Furthermore, as a result of in situ encapsulation of the PAL matrix and defect passivation caused by H-bonding and coordination-bonding interaction, the CsPbBr3@PAL antenna in water shows a substantially enhanced photoluminescence quantum yield (36.2%) and longer lifetime. After sequentially assembling Eosin Y and Rose Bengal in the pores of the PAL matrix, RB-ESY-CsPbBr3@PAL with a sequential two-step efficient Förster resonance energy transfer process exhibited extremely enhanced photocatalytic activity toward Friedel–Crafts alkylation reactions in aqueous solution, 2.5-fold higher than that of corresponding ESY/RB. Our work provides a feasible strategy for the exploitation of ultra-stable halide perovskite-based ALHSs in aqueous media for solar-energy conversion.


Materials:
All reagents and deuterated chloroform were commercially available unless otherwise stated. The reagents and solvents were dried according to the standard procedures described in literature. X-ray diffraction (PXRD) patterns were recorded on AXS D8-Advanced diffractometer with Cu Ka radiation. The nitrogen adsorption-desorption isotherms were acquired through a high precision Autosorb apparatus at 77.35 K, and Non-Local Density Functional Theory (NLDFT) method was applied to the adsorption branch to calculate the pore size distribution of samples. X-ray photoelectron spectroscopy (XPS, a PHI-5702 multifunctional spectrometer) measurements were investigated using Al Kα radiation. Fourier transform infrared (FTIR) spectra were performed on a Nicolet FT-170SX spectrometer at room temperature. Ultraviolet and visible absorption (UV-vis) measurements were recorded on Shimadzu UV-1750 at room temperature. UV/Vis diffuse reflectance spectroscopy (DRS) were measured on a UV-2006 UV-Specterophotometer. Photocatalysis was performed using Xenon lamp (HSXF/UV 300), equipped with 400-800 nm filter. Photoluminescence (PL) spectra were acquired on an Edinburgh Instruments FLS920 fluorescence spectrometer. 1 H-NMR spectra were recorded in CDCl 3 on a JEOL ESC 400 MHz instrument. Chemical shifts for 1 H-NMR spectra are reported in parts S5 per million (ppm, δ scale) downfield from tetramethylsilane, and referenced internally to the residual proton in the solvent (CDCl 3 : δ 7.26). Data are reported as follows: Chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), coupling constants. J, are reported in hertz.
The absolute quantum yields were measured on a horiba fl-3 instrument with the integrating sphere.
Time-resolved PL decay curves were measured on a horiba fl-3 instrument and fitted to a biexponential (see eqs S1 and S2) decay curves of eq S1 The average lifetimes were calculated using eq S2 = ( 1 1 2

Synthesis of Cs-Oleate.
Cs-Oleate (CsOA) was synthesized according to the previous literature and slightly modified. [1] Oleic acid (2.5 mL), octadecene (10 mL, ODE) and oleylamine (0.1 mL) were syringed into a 100 mL 3-neck flask containing 0.814 g of Cs 2 CO 3 (2.50 mmol). The resulting mixture was dried at 120 °C for 1 h and then reacted at 150 °C under N 2 atmosphere for 2h. Since CsOA will precipitate out of ODE at room temperature, it has to be preheated to dissolve before usage.

Preparation of CsPbBr 3 QDs without PAL matrix.
In a typical preparation of CsPbBr 3 quantum dots (QDs) without PAL matrix. DMF (1 mL) and PbBr 2 (0.05 mmol) were loaded into a 5 mL flask. After complete solubilization of PbBr 2 , Cs-oleate solution (0.05 mL, 0.4 mol/L in ODE, prepared as shown in above) was added. Finally, 0.05 mL of mixed solution was added into a new flask along with dried PhMe (2 mL).

Photostability and thermostability of CsPbBr 3 @PAL antenna
To evaluate the photostability of the prepared CsPbBr 3 @PAL antenna, the CsPbBr 3 @PAL powder was packed into vial and illuminated with 365 nm LED lamp (10 W) at room temperature. To analyze the thermostability of the synthesized CsPbBr 3 @PAL antenna, the CsPbBr 3 @PAL powder was packed into glass plates with a groove, which was then heated at 150 °C. During the heating-cooling cycle at 30-150°C, photoluminescence (PL) spectra were collected at an interval of 20 °C. [2] The energy-transfer efficiency (Φ ET ) was calculated using equation S3:

Computational Details
In this work, we use first-principles molecular dynamics methods with CP2K/Quickstep [3] to study the collision, adsorption and molecular transfer processes of between water and CsPbBr 3 @PAL. Molecular dynamics algorithm combined with NVT ensemble, Nose-Hover thermostat [4,5] , 1 fs step size, 500,000 steps. The force and velocity are calculated using density functional theory (DFT) [6] for BLYP functional [7] , Gaussian-type basis set [8] and Goedecker-Teter-Hutter (GTH) pseudopotentials [9,10] combined with Gamma k-point and 400 eV cut-off energy. In the calculation steps, the energy minimization is used to balance the system, and then the Maxwell distribution method is used to give the molecules different collision probabilities, and then the dynamic process is carried out. We analyzed the interaction of molecules and substrates using the independent gradient model (IGM) [11] performed by the Multiwfn-3.6 software [12] using the calculated wave function files.  The elemental composition analyses show that content of Mg 2+ , Na + and K + decreased after ion exchange, which further confirmed the occurrence of this process. S13 TEM image shows that the size of CsPbBr3 BCs particles is not uniform, and the particles have holes. The size of CsPbBr3 BCs was estimated by Nano Measurer software and found to almost be in the range of 30-90 nm. S22 S17. Absolute quantum yield measurement Figure S16. Absolute fluorescence quantum yields of CsPbBr 3 @PAL antenna in water. Figure S17. Emission spectra of CsPbBr 3 QDs alone in water.

S8. Size Distribution of as-prepared CsPbBr 3 NCs in
The emission spectra show that the CsPbBr 3 QDs alone are extremely unstable in water, showing negligible fluorescence emission even at concentrations as high as 3.0 mg ml -1 . Therefore, quantum dots alone cannot construct an artificial light-harvesting system in water, which is also the scientific question addressed by this work.
S24 S19. Immersed in water measurements In a 10 mL pyrex glass tube, RB-ESY-CsPbBr 3 @PAL was suspended in 5 mL of H 2 O-MeCN (1:1, v/v) in the presence of indoles (0.2 mmol) and N,N-dimethylaniline (1.0 mmol, 5 equiv). The reaction mixture was stirred and irradiated by Xenon lamp providing visible light (λ > 420 nm) by using a 420 nm cut-off filter. After that, the resulting mixture was centrifuged and washed. The solution was evaporated under reduced pressure, and the obtained crude compound was purified by column chromatography with nhexane/ethyl acetate (20:1) as eluent on silica gel to afford 3-arylmethyl indole derivatives. S34 S29. Illustration of energy level diagram for sequential FRET-associated PL and photocatalytic mechanism Figure S28. Illustration of energy level diagram for sequential FRET-associated PL and photocatalytic mechanism.