at weekends; on weekends；at the weekend；；；
on the weekend; ；
on Saturnday and Sunday;
我们在周末聊了这些话题.
And so it went for the weekend.
；
on the weekend(s),at the weekend(s),over the weekend(s),during the weekend(s)
on Sunday,比较通常的讲法
还有如果指明是哪个周日,如本周日,this Sunday,上周日,last Sunday,直接用,前面不用介词