Oxygen vacancy concentration in metal oxides is crucial to gas sensing performance. This study introduces a novel strategy of oxygen vacancies modulation on CoFe2O4, by two-step controllable incorporation of TiO2@MXene and carbon. In the first step, MXene simultaneously acts as an incorporation agent and a titanium source to grow TiO2 and regulate the oxygen vacancy concentration in CoFe2O4. The fabricated n-n heterojunctions of TiO2/CoFe2O4 further induced a gradient distribution of oxygen vacancies through energy band bending. And a second step, combining glucose as a carbon source, further increases the oxygen vacancy concentration in CoFe2O4 by chemical reduction during a hydrothermal process, leading to the formation of a CoFe2O4-TiO2@MXene-C nanostructured composite. Through controlling the glucose content, the ratio of Co3+ to Co2+ within the composite can be sequentially adjusted, which allows for the further regulation of oxygen vacancy concentration on the composite surface. The effectiveness of this two-step incorporation is demonstrated through enhanced acetone sensing performance, providing valuable insights into the fabrication of high-performance metal oxide-based gas sensors via controlled oxygen vacancy modulation.

The significant in situ multicolored patterning without changing printing tools nor substrate media still remains challenging, especially toward practical applications for anti-counterfeiting. This research invented a unique universal approach for the laser-induced in situ synthesis of colorful fluorescent patterns (from blue: CIE 0.15, 0.18 to red orange: CIE 0.36, 0.39) through the controlled formation of N, S doped carbon dots (CDs) in solid composite polymer films or hydrogel with a hierarchical and physically unclonable microsurface architecture for anti-counterfeiting. The in situ patterning approach, coupled with multi-layer technique, yielding designable blue, yellow, orange, and red orange color under 365 nm in the same pattern. A 5 cm² colorful pattern can be efficiently finished within 5 min without changing the substrate and the line width accuracy can be up to 300 μm. The absolute quantum efficiency of the blue pattern reached as high as 23%. The fluorescent patterns can be survived at indoor for 24 months. The hydrogen bonding interactions between the CDs precursor and polymer facilitated the generation, uniform dispersion and stabilization of CDs during the laser irradiation. The hypothesis that laser irradiation induced photochemical reactions of CD precursors within a polymer matrix was supported by thermodynamic assessments. The universality of in situ fluorescent patterning strategy was demonstrated by developing fluorescent patterns on both solid polymer films, hydrogel, pharmaceutical packaging and textile.

Fluorescent patterns with multiple functions enable high-security anti-counterfeiting labels. Complex material synthesis and patterning processes limit the application of multifunctional fluorescent patterns, so the technology of in situ fluorescent patterning with tunable multimodal capabilities is becoming more necessary. In this work, an in situ fluorescent patterning technology was developed using laser direct writing on solid cellulose film at ambient conditions without masks. The fluorescent intensity and surface microstructure of the patterns could be adjusted by programmable varying of the laser parameters simultaneously. During laser direct writing, carbon dots are generated in situ in a cellulose ester polymer matrix, which significantly simplifies the fluorescent patterning process and reduces the manufacturing cost. Interestingly, the tunable fluorescent intensity empowers the fabrication of visual stereoscopic fluorescent patterns with excitation dependence, further improving its anti-counterfeiting performance. The obtained fluorescent patterns still show ultrahigh optical properties after being immersed in an acid/base solution (pH 5-12) over one month. In addition, the anti-UV performance of the obtained laser-patterned film with transmittance around 90% is comparable to that of commercial UV-resistant films. This work provided an advanced and feasible approach to fabricating programmable, performance-tunable, subtle fluorescent patterns in large-scale for industrial application.