These disyllabic prepositions normally appear at the beginning of a sentence. Their functions are similar to those of conjunctions or to serve as transitions in communication. The following is a list of such disyllabic prepositions that are commonly used.
guān yú (關於): to bring up a new topic
關於我們上次討論的那件事，我已經做了決定了。
guān yú wǒ mén shàng cì tǎo lùn dí nà jiàn shì ， wǒ yǐ jīng zuò liǎo jué dìng le
Regarding the matter we discussed last time, I have already made a decision.
zhì yú (至於): to bring up another topic (that already exists in context)
你說的那兩件事，我贊成第一件事；至於第二件，我還要考慮一下。
nǐ shuō dí nà liǎng jiàn shì ， wǒ zàn chéng dì yī jiàn shì ； zhì yú dì èr jiàn ， wǒ huán yào kǎo lǜ yī xià
About those two matters you mentioned, I support the first one; as to the second, I still need to think about it.
yóu yú (由於): to introduce a reason
Since 由於 is similar in meaning and usage to 因為, it can be followed by a complete sentence. In this case, it functions as a conjunction, not a preposition.
由於種種因素，原來的計畫取消了。(由於 is a preposition.)
yóu yú zhǒng zhǒng yīn sù ， yuán lái dí jì huà qǔ xiāo le
Due to all kinds of factors, the plan has been cancelled.
由於老師生病了，因此我們今天沒有上課。(由於 and 因此 are conjunctive pair.)
yóu yú lǎo shī shēng bìng le ， yīn cǐ wǒ mén jīn tiān méi yǒu shàng kè
Because the teacher was sick, we didn't have class today.
Reference: YUFA! A Practical Guide to Mandarin Chinese Grammar
