Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Summary

A synthesis method for cellulose nanofiber biotemplated palladium composite aerogels is presented.The resulting composite aerogel materials offer potential for catalysis, sensing, and hydrogen gas storage applications.

Abstract

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often result in fragile aerogels with poor shape control. The use of carboxymethylated cellulose nanofibers (CNFs) to form a covalently bonded hydrogel allows for the reduction of metal ions such as palladium on the CNFs with control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Crosslinking the carboxymethylated cellulose nanofibers is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine. The CNF hydrogels maintain their shape throughout synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO₂ supercritical drying. Varying the precursor palladium ion concentration allows for control over the metal content in the final aerogel composite through a direct ion chemical reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in other sol-gel techniques. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metallized palladium porous structure.

Introduction

Aerogels, first reported by Kistler, offer porous structures orders of magnitude less dense than their bulk material counterparts^1,2,3. Noble metal aerogels have attracted scientific interest for their potential in power and energy, catalytic, and sensor applications. Noble metal aerogels have recently been synthesized via two basic strategies. One strategy is to induce the coalescence of pre-formed nanoparticles^4,5,6,7. Sol-gel coalescence of nanop....

Protocol

​CAUTION: Consult all relevant safety data sheets (SDS) before use. Use appropriate safety practices when performing chemical reactions, to include the use of a fume hood and personal protective equipment (PPE). Rapid hydrogen gas evolution can cause high pressure in reaction tubes causing caps to pop and solutions to spray out. Ensure that reaction tubes remain open and pointed away from the experimenter as specified in the protocol.

1. Cellulose nanofiber hydrogel preparation

1. Preparation of cellulose nanofiber solution: Prepare 3% (w/w) cellulose nanofiber solution by mixing 1.5 g of carboxymethyl cellulose nanofibers wi....

Results

The scheme to covalently crosslink cellulose nanofibers with EDC in the presence of ethylenediamine is depicted in Figure 1. EDC crosslinking results in an amide bond between a carboxyl and primary amine functional group. Given that the carboxymethyl cellulose nanofibers possess only carboxyl groups for crosslinking, the presence of a diamine linker molecule such as ethylenediamine is essential to covalently link two adjacent CNFs via two amide bonds. To conf.......

Discussion

The noble metal cellulose nanofiber biotemplated aerogel synthesis method presented here results in stable aerogel composites with tunable metal composition. The covalent crosslinking of the compacted cellulose nanofibers after centrifugation results in hydrogels that are mechanically durable during the subsequent synthesis steps of palladium ion equilibration, electrochemical reduction, rinsing, solvent exchange, and supercritical drying. The hydrogel stability is vital during the electrochemical reduction step given th.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.5 mm platinum wire electrode	BASi	MW-4130	Used for auxillery electrode and separately for lacquer coating and use as a working electrode
1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)	Sigma-Aldrich	1892-57-5
2-(N-morpholino)ethanesulfonic acid (MES)	Sigma-Aldrich	117961-21-4
Ag/AgCl (3M NaCl) Reference Electrode	BASi	MF-2052
Carboxymethyl cellulose, TEMPO Cellulose Nanofibrils, Dry Powder	University of Maine Process Development Center	No 8
Ethanol, 200 proof	PHARMCO-AAPER	241000200
Ethylenediamine	Sigma-Aldrich	107-15-3
Fourier-Transform Infrared (FTIR) Spectrometer, Frontier	Perkin Elmer	L1280044
Hydrochloric Acid	CORCO	7647-01-0
Na2PdCl4	Sigma-Aldrich	13820-40-1
NaBH4	Sigma-Aldrich	16940-66-2
Pd(NH3)4Cl2	Sigma-Aldrich	13933-31-8
Potentiostat	Biologic-USA	VMP-3	Electrochemical analysis-EIS, CV
Scanning Electron Mciroscope (SEM) Helios 600 Nanolab	ThermoFisher Scientific
Supercritical Dryer	Leica	EM CPD300	Aerogel supercritical drying with CO2
Surface and Pore Analyzer	Quantachrome	NOVA 4000e	Nitrogen gas adsorption
Thermal Gravimetric Analysis	TA instruments	TGA Q500
Ultrasonic Cleaner	MTI	EQ-VGT-1860QTD
XRD	PanAlytical	Empyrean	X-ray diffractometry