No abstract

An aqueous-based approach for the scalable synthesis of nitrogen-doped porous carbons with high specific surface area (SSA) and high nitrogen content is presented. Low molecular weight polyacrylonitrile (PAN) is solubilized in water in the presence of ZnCl that also acts as a volatile porogen during PAN pyrolysis to form mesoporous structures with significantly increased SSA. By templating with commercial SiO nanoparticles, nanocellulose fillers or filter paper, nanocarbons with SSA = 1776, 1366, and 1501 m/g, respectively and 10 wt % N content were prepared. The materials formed by this benign process showed excellent catalytic activity in oxygen reduction reaction via the four-electron mechanism.

Copolymer-templated nitrogen-doped carbon (CTNC) films deposited on glassy carbon were used as electrodes to study electrochemically driven hydrogen evolution reaction (HER) in 0.5 M H2SO4. The activity of these materials was extremely enhanced when a platinum counter electrode was used instead of a graphite rod and reached the level of commercial Pt/C electrodes. Postreaction scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements of electrode surfaces revealed that incorporation of even extremely low amounts of Pt resulted in this considerable gain of HER activity. High resolution XPS analysis and density functional theory (DFT) calculations confirmed that pyridinic nitrogen atoms act as active sites for Pt coordination and deposition. The Pt can be incorporated in both molecular (Pt(2+)) and metallic (Pt(0)) form. This study shows that great caution must be taken when designing "metal-free" HER catalysts based on N-doped carbons.

Mussel-inspired polydopamine (PDA) chemistry was employed for the surface modification of ordered mesoporous carbons (OMCs), improving the hydrophilicity, binding ability toward uranium ions, as well as enriching chemical reactivity for diverse postfunctionalization by either surface grafting or surface-initiated polymerization. Uniform PDA coating was deposited on the surface of CMK-3 type OMCs via self-polymerization of dopamine under mild conditions. Surface properties and morphology of the PDA-coated CMK-3 can be tailored by adjusting the dopamine concentration and coating time, without compromising the meso-structural regularity and the accessibility of the mesopores. Due to high density of −NH groups (4.7 μmol/m 2 or 2.8 group/nm 2 ) and −OH groups (9.3 μmol/m 2 or 5.6 group/nm 2 ) of the PDA coating, the modified CMK-3 showed improved hydrophilicity and superior adsorption ability toward uranyl ions (93.6 mg/g) in aqueous solution. Moreover, with the introduction of α-bromoisobutyryl bromide (BiBB) initiator to the PDA-coated CMK-3, we demonstrated for the first time that activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) can be conducted for controlled growth of polymer brushes from the surface of OMCs. Thus, PDA chemistry paves a new way for surface modification of OMCs to create a versatile, multifunctional nanoplatform, capable of further modifications toward various applications, such as environmental decontamination, catalysis, and other areas.

A series of polyacrylonitrile-block-poly(butyl acrylate) (PAN-b-PBA) copolymers were prepared by supplemental activator reducing agent atom transfer radical polymerization (SARA ATRP). These copolymers were then used as precursors to pyrolytic nanostructured carbons with the PAN block serving as a nitrogen-rich carbon precursors and the PBA block acting as a sacrificial porogen. The study revealed that while the size of mesopores can be controlled by the size of the porogenic block, the connectivity of pores diminishes with the decrease of the overall molecular weight of the precursor. This partial loss of mesopore connectivity was attributed to the weaker phase segregation between the blocks of shorter lengths inferred from the shape of small-angle X-ray scattering profiles and from the crystallinity of polyacrylonitrile phase.