The construction of intramolecular homojunction in the carbon nitride framework is one of the advantageous methods to improve photocatalytic performance. Based on the molecular self-assembly strategy to form the intramolecular homojunction, carbon nitride showed enhanced photocatalytic activity. However, the disordered structure of the pristine g-C3N4 obtained using the traditional approach inhibits the dissociation and migration of photocarriers. Here, we adopt a method to prepare the crystalline C3N4 (HCCN) with functional group modifications to form ternary intramolecular homojunction by multistep thermal polymerization. The band structure indicates that cyano and cyanamide-based molecular units in HCCN samples have different highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels, which constitute a special ternary homojunction through the arrangement of energy levels and form an internal electron field in the molecule. The analysis of photoelectron–hole pairs and photocatalytic performance confirms that the ternary structure accelerates the interface charge transfer and reduces reverse charge recombination. Moreover, the compact crystalline structure of HCCN samples greatly improves the dissociation photogenerated charges. Femtosecond transient absorption spectra explain the energy trajectory of charge carrier kinetics of HCCN and confirm that the crystal semiconductor modified by functional groups can promote the dissociation of excitons to free charges. This research provides an idea to obtain crystalline C3N4 of ternary intramolecular homojunctions.

Background There has been no previous report of the prevalence of paediatric oral and maxillofacial pathology in a New Zealand oral pathology diagnostic service. Aim The aim of this study was to review cases of paediatric oral pathology to determine relative frequencies of oral lesions in this age group. Design Paediatric oral pathology cases (≤15 years of age) received between 2007 and 2016 were retrieved from the electronic database of the Oral Pathology Centre, University of Otago. Data collected included diagnoses (categorised into 12 groups), age at diagnosis, and gender. The prevalence of each diagnosis was calculated in terms of percentage of all diagnoses made. Male‐to‐female ratio and mean age at diagnosis were also determined. Results A total of 1139 paediatric cases were identified representing 5.2% of all cases. The most common diagnostic group was salivary gland pathology (25.4%), followed by dental (24.8%) pathology. The most prevalent lesion was mucocoele (23%), followed by dental follicle (14.1%). Malignancies were rare with only two cases identified. Conclusion The findings provide an insight into the prevalence of paediatric oral pathology for clinicians. Mucocoele was the most common diagnosis made, suggesting a high prevalence of soft tissue injury as a main presenting concern warranting diagnosis and management through biopsy.

No abstract

No abstract