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2,5-Furandicarboxylic acid (FDCA) is a promising biobased building block for the synthesis of polymers. In this work, a novel whole-cell biocatalyst was constructed by coexpressing vanillin dehydrogenase (VDH1) and HMF/furfural oxidoreductase (HmfH) in Escherichia coli for cascade catalytic oxidation of 5-hydroxymethylfurfural (HMF) to FDCA under sacrificial substrate-free conditions. HMF was rapidly transformed to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) by VDH1, followed by subsequent oxidation to 5-formyl-2-furancarboxylic acid (FFCA) by HmfH, and finally, FFCA was converted to FDCA by VDH1 and/or HmfH. Under pH-controlled conditions, the biocatalyst enabled efficient synthesis of FDCA from 150 mM HMF in a 96% yield. Besides, FDCA was prepared in the gram scale with a productivity of around 0.4 g/L h.

Furan carboxylic acids are useful chemicals in various industries. In this work, biocatalytic production of furan carboxylic acids was reported with high productivities by cofactor‐engineered Escherichia coli cells. NADH oxidase (NOX) was introduced into E. coli harboring aldehyde dehydrogenases (ALDHs) to promote intracellular NAD+ regeneration, thus significantly enhancing ALDH‐catalyzed oxidation. These engineered biocatalysts were capable of efficient aerobic oxidation of a variety of aromatic aldehydes. More importantly, they exhibited high substrate tolerance toward toxic furans. E. coli co‐expressing vanillin dehydrogenase and NOX (E. coli_CtVDH1_NOX) enabled efficient oxidation of 250 mM of 5‐hydroxymethylfurfural (HMF) to 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA), providing a productivity of 3.7 g/L h. With E. coli_CtVDH2_NOX as catalyst, up to 240 mM of furfural and 5‐methoxymethylfurfural (MMF) could be smoothly oxidized. 2‐Furoic acid (FCA, 227 mM) and 5‐methoxymethyl‐2‐furancarboxylic acid (MMFCA, 287 mM) were produced in fed‐batch synthesis, providing the productivities of 2.0 and 5.6 g/L h, respectively.

TiO (Degussa P25) photocatalysts harboring abundant oxygen vacancies (Vacuum P25) were manufactured using a simple and economic Vacuum deoxidation process. Control experiments showed that temperature and time of vacuum deoxidation had a significant effect on Vacuum P25 photocatalytic activity. After 240 min of visible light illumination, the optimal Vacuum P25 photocatalysts (vacuum deoxidation treated at 330 °C for 3 h) reach as high as 94% and 88% of photodegradation efficiency for rhodamine B (RhB) and tetracycline, respectively, which are around 4.5 and 4.9 times as that of pristine P25. The XPS, PL and EPR analyses indicated that the oxygen vacancies were produced in the Vacuum P25 during the vacuum deoxidation process. The oxygen vacancy states can produce vacancy energy level located below the conduction band minimum, which resulting in the bandgap narrowing, thus extending the photoresponse wavelength range of Vacuum P25. The positron annihilation analysis indicated that the concentrations ratio of bulk and surface oxygen vacancies could be adjusted by changing the vacuum deoxidation temperature and time. Decreasing the ratio of bulk and surface oxygen vacancies was shown to improve photogenerated electron-hole pair separation efficiency, which leads to an obvious enhancement of the visible photocatalytic activities of Vacuum P25.

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